Skincare Ingredients

Sodium Sulfite

Sodium sulfite is primarily used as an antioxidant/preservative in low concentrations, but sulfites are well-documented to cause irritation and allergic-type reactions in a subset of sensitive individuals, with positive patch-test reactions reported (especially in eczematous skin). While many users tolerate it, the risk is meaningfully higher than baseline for compromised barriers and reactive populations, so I score it as a moderate irritant where patch testing is prudent. Safety Notes: In consumer skincare, sodium sulfite is most often used as an antioxidant/reducing agent (oxygen scavenger) to protect oxidation-sensitive actives and fragrances; at the low end it appears around ~0.05–0.2% in leave-on serums/creams and some rinse-off cleansers mainly for stabilization. Higher-strength OTC products (especially rinse-off cleansing systems, exfoliating/brightening products, and some self-tan/anti-oxidation specialty formulas) can use it around ~0.5–2.0% to provide stronger reducing/antioxidant and anti-browning effects, with >2% being uncommon in mainstream consumer skincare due to odor/irritation and sulfite-sensitivity considerations.

Sodium Tallowate

Sodium tallowate is a soap (alkaline fatty acid salt) typically used at high concentrations in bar cleansers, where its naturally high pH and surfactant action can disrupt the stratum corneum and increase transepidermal water loss. Clinically, true allergy is uncommon, but irritant contact dermatitis and eczema flares are well-documented in sensitive skin due to barrier disruption, especially with frequent use or compromised skin. Given its routine use level and predictable irritancy in atopic/reactive populations, it warrants a notable irritancy score. Safety Notes: Sodium tallowate is a primary soap base in traditional bar soaps and some shave soaps; in such products it commonly appears at very high levels (often the dominant fatty-acid sodium salt fraction), with consumer-available bars reaching roughly 60–85% of the finished product (balance being water, glycerin, other fatty acid salts, fragrance, chelants, etc.). At the low end, it is occasionally used in blended surfactant systems (e.g., certain liquid/cream cleansers or syndet-style hybrids, or as a minor structurant/foam modifier) where it can appear around ~0.1–1%. This is essentially a rinse-off ingredient in mainstream use; meaningful leave-on use is uncommon due to alkalinity/irritation and soap instability in leave-on emulsions.

Sodium Trideceth Sulfate

Sodium Trideceth Sulfate is an anionic sulfate surfactant used primarily for cleansing/foaming, typically in rinse-off products where it can still disrupt stratum corneum lipids and increase transepidermal water loss. Sulfate surfactants are consistently associated with higher irritation in patch testing and real-world use, with risk amplified in eczema, barrier-compromised, or facial skin even at standard cleanser concentrations. Given its surfactant class and barrier-stripping potential, I score it as a significant irritant requiring caution for sensitive populations. Safety Notes: Sodium Trideceth Sulfate is primarily used as an anionic surfactant in rinse-off cleansing products; at the low end (~0.5–2%) it appears in mild facial cleansers and syndet-style washes where it is blended with amphoterics/nonionics to reduce irritation while still boosting foam and detergency. The high end (~10–15% active) is observed in stronger, consumer-available clarifying shampoos, body washes, and some acne/oily-skin cleansers where higher surfactant actives are used for enhanced soil/sebum removal. It is rarely used in leave-on products (functionally impractical due to irritation and residue), so the observed market range is effectively for rinse-off formulations.

Solanum Lycopersicum Fruit Extract

Solanum Lycopersicum (tomato) fruit extract is primarily used as an antioxidant/soothing botanical at low concentrations, but botanicals contain multiple bioactive compounds (including acids and glycoalkaloid traces) that can trigger stinging or dermatitis in reactive or eczema-prone skin. Patch-test and clinical experience show plant extracts are a common source of unpredictable irritation or sensitization compared with inert humectants, especially when used cumulatively in multi-extract formulas. Given the variability of extract composition and the higher risk profile in compromised skin, a mild irritancy score is the safest clinically-aligned assessment. Safety Notes: In mass-market leave-on skincare, Solanum Lycopersicum (Tomato) Fruit Extract is frequently used as a secondary antioxidant/soothing botanical at very low levels (often ~0.0005–0.1%) within blended “fruit/vegetable extract” systems and fragrance-color masking complexes. Higher concentrations are seen in botanical-forward serums, masks, and ampoules where the extract is a key story ingredient; depending on solvent system (glycerin/butanediol/water) and extract potency, consumer products can reach ~1–10% of the commercial extract solution. Rinse-off cleansers and masks typically sit at the lower-to-mid part of the range for cost and stability/odor reasons, while leave-on treatments more often occupy the upper end.

Solanum Melongena Fruit Extract

Solanum melongena (eggplant) fruit extract is primarily used as an antioxidant/soothing botanical at low concentrations (typically well under 1–2%) and is generally well tolerated in leave-on products. However, as a plant extract containing multiple phenolic compounds, it carries a small but real risk of irritant reactions or botanical allergy in highly reactive or eczematous patients, especially when layered with other actives. Given the limited robust irritation-patch data compared with core emollients/humectants, I score it as gentle but not “very gentle.” Safety Notes: In commercial skincare, Solanum melongena (eggplant) fruit extract is most often used as a minor botanical/antioxidant support ingredient in multi-extract blends, where finished-product levels commonly fall in the ~0.0005–0.1% range (especially in leave-on serums/lotions and rinse-off cleansers using low-dose label-claim botanicals). Higher concentrations are seen in consumer-available “single-hero” botanical gels/serums and some K-beauty style extracts/ampoules where the extract (typically supplied in a solvent like glycerin/butanediol/water) can be dosed around 1–5% in leave-on products; above this is uncommon due to odor/color, tack, and cost rather than regulatory limits.

Solidago Virgaurea Extract

Solidago virgaurea (European goldenrod) extract is a botanical anti-inflammatory/soothing ingredient typically used at low percentages, but it contains multiple plant secondary metabolites (e.g., flavonoids/phenolics) that can trigger irritation or allergic contact dermatitis in a small yet clinically meaningful subset of reactive/eczema-prone patients. Patch-test literature and real-world sensitization patterns for botanicals support a non-zero risk, especially with leave-on use and in compromised barriers. Given patient-safety priorities and the unpredictability of botanical extract composition, I rate it as mild with occasional sensitivity possible. Safety Notes: In mass-market leave-on skincare, Solidago virgaurea (goldenrod) extract is most often used as a minor soothing/antioxidant botanical within blended complexes or at the end of the INCI list, corresponding to trace-to-low levels around 0.0001–0.1%. Mid-range usage (0.1–1%) appears in toners/serums/creams positioned for calming or anti-redness benefits, while the highest consumer-available levels (~1–5%) are typically found in niche “single-hero” botanical serums/ampoules and some rinse-off masks/cleansers where higher botanical loading is feasible; actual deliverable actives depend strongly on extract type and solvent ratio (e.g., glycerin/propylene glycol extracts vs dry extracts).

Soluble Collagen

Soluble collagen (typically hydrolyzed collagen) is a film-forming, humectant/conditioning protein used in low-to-moderate concentrations (~0.1–5%) and is generally well-tolerated on skin. Clinical and patch-test experience suggests irritation is uncommon, but as a protein-derived material it can occasionally trigger stinging or contact reactions in highly reactive or eczema-prone individuals, so it is not fully “inert.” Safety Notes: In mass-market lotions, toners, and facial serums, soluble collagen (hydrolyzed/solubilized collagen as a film-forming humectant) is often used at low “label-claim” levels around 0.05–0.5%, especially in multi-active leave-on products. Higher-strength consumer-available products (collagen serums/ampoules, sheet-mask essences, and some “collagen cream” concentrates) commonly use ~1–3%, with the upper end around 5% where viscosity, odor, tack, and stability constraints typically limit further increases. Rinse-off cleansers may use similar or slightly lower levels due to limited benefit from short contact time, while leave-on formats more often reach the high end.

Soluble Proteoglycan

Soluble proteoglycans are high–molecular weight skin-conditioning/humectant biopolymers typically used at low percentages in leave-on products, and they are generally well tolerated with low rates of irritation in routine cosmetic use. However, as a protein/glycosaminoglycan complex (often marine- or animal-derived), there is a small but real risk of sensitization in highly reactive or eczema-prone patients, so it cannot be considered completely inert. Given typical concentrations and the need to err on patient safety, it best fits a very gentle (0.2) profile rather than exceptionally gentle or inert. Safety Notes: In commercial leave-on products (serums, ampoules, creams), soluble proteoglycan is most often used as a low-level “bioactive” in the 0.001–0.1% range, consistent with supplier active solutions where the INCI appears near the end of the list. High-strength consumer-available products (especially Japanese “proteoglycan” essences/ampoules and concentrated booster serums) can reach roughly 1–3% active, with higher levels being uncommon due to raw material cost, viscosity/film-forming effects, and stability/odor constraints. Use in rinse-off products is typically lower (often ≤0.05%) because contact time is short and deposition is limited.

Sophora Angustifolia Root Extract

Sophora angustifolia root extract is a botanical extract used for soothing/brightening and anti-inflammatory claims (often at ~0.1–2%), but it contains bioactive alkaloids and flavonoids that can trigger irritant or allergic contact dermatitis in a subset of sensitive users. Clinical patch-test literature on this specific extract is limited and “plant extract” reactions are a recurrent pattern in eczema-prone patients, especially with leave-on products and compromised barriers. Given the uncertainty and the real-world sensitization potential of botanicals, I score it as mild irritancy rather than assuming it is inherently gentle. Safety Notes: In mass-market and prestige leave-on products (brightening/soothing serums, lotions, and toners), Sophora Angustifolia Root Extract is often used as a minor botanical support ingredient at very low levels (~0.001–0.05%), especially when supplied as a dilute glycerin/butylene glycol extract. Higher-strength consumer products (targeted spot treatments, concentrated serums, and some K-beauty brightening formulas) can use the extract at 1–5% when the trade material is a standardized liquid extract or when marketed as a hero botanical, with 5% representing the upper end seen in OTC leave-on formulations; rinse-off products typically sit toward the low end due to brief contact time.

Sorbeth-230 Tetraoleate

Sorbeth-230 tetraoleate is a high–molecular weight nonionic surfactant/solubilizer used in leave-on and rinse-off products (often around ~0.1–5%) to help disperse oils and improve texture. Nonionic ethoxylated emulsifiers like this are generally well tolerated, but they can still cause mild barrier disruption or stinging in highly reactive or eczematous skin, especially when layered with other surfactants or actives. Overall clinical experience and patch-test profiles support a low irritation potential, but not truly inert, so a gentle (not exceptionally gentle) score is most consistent with patient-safety caution. Safety Notes: Sorbeth-230 Tetraoleate is used primarily as a lipophilic solubilizer/emulsifier for oils, fragrances, and cleansing oils, and in many commercial leave-on lotions/serums it appears at low use levels (~0.1–2%) to help stabilize oily phases or improve sensory. Higher concentrations are observed in consumer-available cleansing oils, balm-to-oil cleansers, and high-oil makeup removers where it can function as a main self-emulsifying surfactant system (~5–20%), especially in anhydrous formats that must rinse clean. No specific global maximum is established in major cosmetic regulations for this non-restricted ingredient, so upper-end use is typically constrained by irritation potential and product aesthetics rather than regulatory limits.

Sorbeth-30 Tetraoleate

Sorbeth-30 Tetraoleate is a nonionic surfactant/solubilizer and emulsifier used at low percentages (often ~1–10%) to disperse oils and pigments, and it is generally well-tolerated compared with harsher anionic surfactants. However, as a solubilizer it can increase penetration of other lipophilic substances and may cause mild stinging or barrier disruption in highly reactive or eczema-prone skin, especially in leave-on cleansing balms/oil-based systems. Given its overall low intrinsic reactivity but real potential to contribute to irritancy in compromised skin, a gentle (not “very gentle”) score is most consistent with patient-safety considerations. Safety Notes: Sorbeth-30 Tetraoleate is used as a nonionic emulsifier/solubilizer for high-oil systems and in cleansing oils/balms and microemulsions; in many leave-on emulsions and makeup removers it appears at low support levels around 0.1–1% to aid solubilization and stability. In consumer oil cleansers, balm-to-oil cleansers, and anhydrous/microemulsified makeup remover formats, it is commonly used at 2–10%, with high-strength specialty OTC products reaching ~12–15% to solubilize heavy oils and pigments while maintaining rinseability.

Sorbic Acid

Sorbic acid is an antimicrobial preservative typically used around ~0.1–0.3% (sometimes higher depending on pH), and it can sting and irritate, especially in leave-on products and on compromised barriers. Patch testing and clinical experience show it can provoke irritant reactions and occasional allergy in reactive/eczema-prone patients, so I score it as a moderate-risk preservative where patch testing is prudent. Safety Notes: In commercial skincare, sorbic acid is most often used as a preservative/acidifier at very low levels, with leave-on and rinse-off products commonly starting around ~0.01–0.05% when paired with other preservative systems. Higher-strength consumer-available formulations (e.g., “preservative-free”-leaning systems relying more heavily on sorbic acid, low-pH gels/toners, and some natural/organic emulsions) can reach ~0.2–0.6% to achieve antimicrobial support, though performance is pH-dependent and typically strongest in acidic formulas (often used alongside potassium sorbate and/or benzoic acid). This range reflects observed OTC market use; practical upper limits are usually driven by solubility, odor/sensory impact, and irritation risk rather than a single global maximum.

Sorbitan Isostearate

Sorbitan isostearate is a nonionic emulsifier/surfactant typically used at low concentrations (about 0.5–5%) to stabilize creams and lotions, and it is generally well-tolerated in clinical and consumer use. However, as a surfactant/emulsifier it can contribute to barrier disruption or mild irritation in highly reactive or eczematous skin—especially in leave-on products used repeatedly—so it is best classified as gentle rather than exceptionally gentle. Safety Notes: Sorbitan isostearate is most often used as a W/O emulsifier/co-emulsifier or dispersant, and in many leave-on creams/lotions it appears at low levels (~0.1–1%) as part of an emulsifier system; the lowest observed uses in commercial products are around 0.05% as a minor stabilizer or pigment/UV filter wetting aid. High-strength consumer products such as water-in-oil sunscreens, heavy barrier creams, cleansing oils/balms, and some makeup/primer-type emulsions can use it at ~3–8% to build and stabilize the oil-phase structure; higher levels are uncommon due to sensory (waxy/drag) and emulsification balance constraints. No specific EU/FDA maximum applies for this ingredient in cosmetics beyond general safety, so the upper bound is driven by formulation performance and tolerability rather than regulation.

Sorbitan Laurate

Sorbitan laurate is a nonionic surfactant/emulsifier used at low concentrations (typically ~0.5–5%) to solubilize and stabilize formulations, and it is generally well-tolerated compared with harsher anionic surfactants. Patch-test data and clinical experience suggest low but real irritation potential, especially in compromised barriers (eczema/post-procedure) where surfactant exposure can increase stinging or dryness. Given cumulative exposure in multi-step routines and my caution for highly reactive patients, it fits best as a gentle ingredient with minimal but nonzero risk. Safety Notes: Sorbitan laurate is a nonionic emulsifier/co-emulsifier and dispersant that shows up at very low levels (~0.05–0.3%) in leave-on lotions/serums primarily as a supporting emulsifier or solubilizer within multi-emulsifier systems. In richer creams, cleansing creams, and some rinse-off surfactant systems it is commonly used around ~0.5–3% to build/steady O/W emulsions and improve texture. High-strength consumer products (e.g., heavy barrier creams, anhydrous-to-aqueous self-emulsifying balms, or very high oil-load emulsions) can reach ~5–8% as part of the primary emulsifier blend; higher is uncommon in OTC cosmetics due to feel, potential waxy drag, and diminishing returns on stability.

Sorbitan Oleate

Sorbitan oleate is a nonionic emulsifier/surfactant typically used at low percentages (often ~0.5–5%) to stabilize oil-in-water systems; it is generally well-tolerated compared with harsher anionic surfactants. However, as a surfactant/emulsifier it can still contribute to barrier disruption and provoke mild stinging or dermatitis in highly reactive or eczema-prone skin, especially in leave-on products or when combined with other irritants. Given its low intrinsic reactivity but real potential to irritate compromised skin, it fits best as a gentle ingredient with minimal but non-zero risk. Safety Notes: Sorbitan oleate is typically used as a W/O emulsifier, co-emulsifier, or dispersant and is often present at low levels (~0.05–0.5%) in leave-on creams/lotions and some rinse-off cleansers as part of an emulsifier blend. Many commercial emulsions and cleansing oils/balms use it around 1–5% to stabilize the oil phase and aid self-emulsification. The upper end (~8–10%) is observed in high-oil, water-in-oil, or self-emulsifying oil cleanser/balm formats sold OTC where higher emulsifier loading is needed; higher levels are generally limited by sensorial drag/greasiness and potential irritation rather than explicit regulatory maximums.

Sorbitan Oleate Decylglucoside Crosspolymer

Sorbitan Oleate Decylglucoside Crosspolymer is a polymeric non-ionic surfactant/emulsifying and solubilizing agent typically used at low levels (often <1–3%) to stabilize formulas and improve sensorial properties. Decyl glucoside–based materials can still provoke stinging or barrier disruption in a subset of highly reactive or eczematous patients (especially in leave-on products or when combined with other surfactants), but crosspolymerization generally reduces free surfactant activity and lowers irritation risk compared with simple surfactants. Overall it is usually well tolerated, yet not inert, so I score it as gentle with a small but real irritation potential in compromised skin. Safety Notes: Sorbitan Oleate Decylglucoside Crosspolymer is a polymeric emulsifier/rheology modifier typically used at low levels to stabilize O/W emulsions and improve sensory/viscosity; in mainstream leave-on lotions/creams it is commonly seen around ~0.1–1%. The lowest market-observed use levels (~0.05%) occur where it is a secondary stabilizer in multi-emulsifier systems, while higher-strength consumer-available products (notably anhydrous-to-aqueous transforming balms/gel-creams, high-oil-load cleansers, and specialty texture systems) can use it up to about ~5% to build structure and stabilize challenging phases. No specific FDA/EU maximum applies for this ingredient as such; practical upper limits are driven by texture, potential soaping/tack, and compatibility with oils/surfactants, with rinse-off formats generally tolerating the upper end more readily than leave-on.

Sorbitan Olivate

MVP Approved - Sorbitan Olivate is a gentle, olive-derived emulsifier commonly used to stabilize skincare formulations with a low risk of irritation.

Sorbitan Sesquioleate

Sorbitan sesquioleate is an emulsifier/surfactant typically used at low percentages, but it has a well-documented history as a clinically relevant contact allergen (used as a marker in patch testing and associated with sensitization from topical products). In sensitive-skin and eczema populations, even low-level exposure can trigger allergic contact dermatitis and barrier disruption, so its real-world irritation/sensitization risk is significant despite “functional” use concentrations. Safety Notes: Sorbitan sesquioleate is primarily used as a W/O emulsifier and solubilizing/co-emulsifying surfactant; in many mass-market leave-on creams/lotions it appears at low levels (~0.05–0.5%) to assist emulsification and improve pigment/fragrance or oil-phase compatibility. Higher levels (typically ~2–5%) are observed in richer W/O barrier creams, foundations/tinted products, and specialty emulsions where it is a principal emulsifier and can also help disperse challenging oil phases. The upper end (~6–8%) is seen in niche/high-load W/O formulations available OTC (e.g., very water-resistant barrier creams or heavy W/O makeup bases), while noting it can be a known sensitizer in some populations so many brands formulate below 1% in leave-on products.

Sorbitan Stearate

Sorbitan Stearate is a non-ionic emulsifier used typically around 0.5–5% in creams and lotions and is generally well tolerated, including in products intended for sensitive skin. Human patch testing and clinical use suggest a low rate of irritation and sensitization compared with many surfactants, though rare reactions can occur in highly reactive or eczema-prone patients, especially on compromised skin. Safety Notes: Sorbitan stearate is widely used as a nonionic emulsifier/co-emulsifier and structurant, and in commercial leave-on creams/lotions it often appears at low levels (~0.05–1%) to support emulsion stability alongside other emulsifiers. Higher levels (3–10%) are observed in consumer-available anhydrous cleansing balms, cold-cream type makeup removers, and high-oil W/O or hybrid systems where it also contributes body and pigment wetting; rinse-off products typically sit in the low-to-mid part of the range due to feel and rinsability constraints. There is no specific EU/FDA maximum for sorbitan stearate in cosmetics, so practical stability/sensory limits largely define the upper end in OTC products.

Sorbitol

Sorbitol is a sugar alcohol used primarily as a humectant in leave-on and rinse-off products (often ~1–10% or higher) and is generally well tolerated, including in sensitive-skin formulations. Clinical experience and patch-test data suggest irritation is uncommon, but it can occur in highly reactive or barrier-impaired skin (e.g., eczema) due to osmotic effects or formulation-dependent factors. Given its broad safety profile but non-zero risk in compromised skin, it fits “very gentle” rather than fully inert. Safety Notes: In commercial skincare, sorbitol is often used at very low levels (~0.05–1%) as a secondary humectant/sweetener or processing aid in leave-on creams/serums and rinse-off cleansers. Mainstream moisturizers, toners, and face washes commonly use ~1–10% for humectancy and feel, while high-strength consumer products such as glycerin/sorbitol humectant gels, some hand/body gels, and certain clear soap or cleansing bar bases can reach ~30–70% sorbitol (often alongside other polyols), with the upper end more typical for rinse-off or high-solids gel/bar formats than elegant leave-on facial products.

Soy Isoflavones

Soy isoflavones are antioxidant/phytoestrogenic actives typically used at low percentages in leave-on products, where they are generally well-tolerated but not completely inert. In patch testing and real-world use, soy-derived actives can trigger irritation or allergic contact dermatitis in a minority of sensitive or atopic individuals due to residual soy proteins/extract complexity and individual allergy history. Given the potential for delayed sensitization in highly reactive eczema-prone patients, I rate them as mild rather than gentle. Safety Notes: In commercial skincare, soy isoflavones are most often delivered via soybean extract blends, with finished-product isoflavone levels commonly landing around 0.01–0.2% in mass-market moisturizers/eye creams and anti-aging serums (low end driven by cost, color/odor constraints, and use as a supporting antioxidant/brightening active). Higher-strength consumer-available “isoflavone” or “genistein/daidzein” targeted treatments can reach about 0.5–2.0% total soy isoflavones in leave-on products, generally using standardized extracts or purified fractions to maintain stability and aesthetics. Rinse-off products typically sit at the lower end because of short contact time and reduced incentive to load actives.

Spermidine

Spermidine is a naturally occurring polyamine used in skincare mainly as an anti-aging/cell-support ingredient, typically at low concentrations (often well under 1%). While not a classic irritant like acids or retinoids, polyamines are biologically active and can sting or provoke reactivity in compromised barriers (e.g., eczema, post-procedure) even when overall tolerability is good in the general population. Given limited large-scale human irritation datasets in highly sensitive cohorts and the need to err on patient safety, I rate it as mild with occasional sensitivity possible. Safety Notes: In consumer skincare, spermidine is typically used as a low-dose bioactive/anti-aging claim ingredient, most often in leave-on serums and creams at microdose levels (commonly around 0.001–0.05%), with some products listing it near the end of the INCI at ~0.0001% as part of multi-active complexes. High-strength niche formulations marketed for “cell renewal/autophagy” can reach the low tenths of a percent, with the upper end around ~0.5% limited by odor, stability (oxidation/amine reactivity), and irritation/tack risks; rinse-off uses are rare and generally lower due to short contact time. There is no specific FDA/EU maximum limit established for spermidine in cosmetics, so observed market practice and formulation constraints primarily set the range.

Sphingolipids

Sphingolipids are skin-identical barrier lipids (related to ceramides) used at low levels in moisturizers/repair products to support stratum corneum function, and they are generally well-tolerated in sensitive and eczema-prone skin. Clinical experience and patch-test data suggest low inherent irritation potential, with most reactions attributable to the overall formula rather than the sphingolipids themselves. I score them as very gentle (not inert) to account for rare intolerance in highly reactive patients and the fact they are bioactive lipids rather than purified water. Safety Notes: In commercial skincare, sphingolipids are most often used as ceramide/sphingolipid complex actives and appear at very low levels (about 0.001–0.05%) in mass-market moisturizers, cleansers, and barrier-repair lotions where they function as supportive lipids rather than primary actives. Mid-to-high end leave-on barrier creams and serums commonly position them around 0.05–0.5%, while a small number of high-strength OTC barrier concentrates (typically anhydrous balms or lamellar/emulsion systems) reach about 1–2% total sphingolipids. Rinse-off formats generally sit at the low end due to cost and deposition limits; there is no specific FDA/EU maximum, so the upper bound is driven mainly by solubility, lamellar structure stability, and sensory constraints.

Sphingomonas Ferment Extract

Sphingomonas ferment extract is a bioferment/skin-conditioning ingredient used at low levels (typically <1–2%) to support barrier function and hydration, and it is generally well-tolerated in sensitive-skin formulas. Clinical irritation signals are uncommon, but as a fermentation-derived complex it can contain trace residuals that very reactive or eczema-prone patients may occasionally react to, so it is not truly inert. Given its usual low concentration and low documented irritancy, it fits best as very gentle rather than completely non-irritating. Safety Notes: In commercial skincare, Sphingomonas Ferment Extract is most often used as a bioferment/soothing or skin-conditioning active dosed very low (often in the 0.0005–0.05% range in leave-on creams/serums when supplied as a concentrated active or as part of a multi-ingredient complex). Higher-strength consumer products (typically leave-on serums, ampoules, and “microbiome”/barrier concentrates) can reach ~1–5% when the INCI reflects the ferment extract as a primary functional component rather than a trace component of a blend; rinse-off products generally sit toward the low end due to short contact time. No specific EU/FDA maximum is set for this INCI, so the upper end is constrained mainly by supplier guidance, sensorial limits, and stability/preservation requirements rather than regulation.

Spilanthes Acmella Flower Extract

Spilanthes acmella (often marketed as “botox-like”) is a botanical extract used in low percentages for smoothing/firming, but it contains bioactive alkamides (e.g., spilanthol) that can be irritating and has documented potential for contact dermatitis in sensitized individuals. As with many plant extracts, variability in composition and the presence of multiple reactive constituents increases unpredictability for eczema-prone or highly reactive skin, especially with leave-on use. Given the non-essential benefit and real, if infrequent, irritation/sensitization risk, it is best classified as mild rather than gentle. Safety Notes: In commercial leave-on products (anti-wrinkle/“instant tightening” serums, eye creams, moisturizers), Spilanthes acmella flower extract is frequently used at very low levels (≈0.01–0.1%) as a marketing/booster botanical within a multi-extract complex, consistent with typical supplier recommended-use ranges and INCI-list positioning. Higher-strength consumer products—especially “botox-like” or firming concentrates and ampoules—are observed using ~1–3% extract, with a practical upper market end around 5% for standardized extracts before odor, color, and stability/skin-feel constraints become limiting; rinse-off formats generally sit at the low end because contact time is short.

Spinacia Oleracea Leaf Extract

Spinacia Oleracea (spinach) leaf extract is primarily used as an antioxidant/soothing botanical at low concentrations in leave-on products, and it is generally well-tolerated. However, like many plant extracts, it contains multiple bioactive compounds and trace impurities that can trigger irritant or allergic contact reactions in a minority of highly reactive or eczematous patients, especially on compromised skin. Given this non-zero but typically low risk profile, it fits best as a "gentle" ingredient rather than exceptionally gentle/inert. Safety Notes: In mainstream consumer leave-on skincare (serums, creams, masks) spinach leaf extract is often used as a minor antioxidant/soothing botanical at trace-to-low levels around 0.0005–0.1%, especially when supplied as a dilute glycerin/propylene glycol extract or part of a botanical blend. Higher-strength consumer products marketed around “superfood/greens” or antioxidant concentrates can use the extract at ~1–5% (typically as a standardized supplier extract solution), with 5% representing the upper end commonly seen before cost, odor/color, and stability constraints become limiting; rinse-off products typically sit toward the low end due to reduced contact time.

Spiraea Ulmaria Extract

Spiraea ulmaria (meadowsweet) extract is a botanical anti-inflammatory/astringent ingredient typically used at low concentrations, but it contains salicylate-related constituents and polyphenols that can sting compromised skin and can trigger reactions in salicylate-sensitive or highly atopic individuals. Clinical patch-test data for this specific extract is limited and botanical extracts show variable composition, so I score it as a moderate irritant/allergen risk rather than “gentle,” especially in eczema-prone populations and when layered with other actives. Safety Notes: In mass-market and prestige skincare, Spiraea ulmaria (meadowsweet) extract is most often used as a minor soothing/astringent botanical at very low label-levels (often as part of a larger botanical blend), with observed use down to ~0.0001% in complex formulas where it appears near the end of the INCI list. At the high end, a few consumer-available “high-botanical” toners/serums and clarifying products using concentrated glycerin/propylene glycol extracts can reach ~1–5% as a single extract input; above this is uncommon due to odor/color, polyphenol/tannin-related sensorial issues, and stability/compatibility constraints (leave-on typically tops out lower than rinse-off, but the market maximum is seen in leave-on toners/serums).

Spirulina Maxima Extract

Spirulina maxima extract is primarily used as an antioxidant/soothing botanical at low-to-moderate concentrations, but algae-derived extracts contain complex proteins and pigments that can trigger irritation or allergy in a minority of sensitive or eczema-prone patients. Human patch-test and real-world reports for algae/botanical extracts show generally good tolerability yet non-zero rates of irritant or allergic reactions, especially on compromised skin or when combined with other actives. Given the unpredictability of botanical extract composition and the higher risk in reactive skin populations, a mild (0.4) score is the safer clinically-aligned assessment. Safety Notes: In mass-market leave-on products (serums, creams, eye products) spirulina maxima extract is frequently used as a label-support/antioxidant claim ingredient at very low levels (~0.001–0.1%), consistent with typical supplier-recommended use rates for algae extracts and the low sensory tolerance (color/odor) of spirulina. Higher-concentration consumer products (mask packs, algae-focused gels/creams, and some natural/DIY-positioned items) can reach ~1–5% extract (or extract solids equivalent) before color, odor, and stability/compatibility become limiting; rinse-off masks more commonly tolerate the upper end than clear leave-on formats. There is no specific EU/FDA maximum for spirulina extract in cosmetics, so the observed range is primarily constrained by aesthetics, microbial control, and formulation stability.

Squalane

MVP Approved - Squalane is a lightweight, plant-derived emollient widely used in skincare for its moisturizing properties and compatibility with most skin types, including sensitive and acne-prone skin.

Squalene

Squalene is a skin-identical emollient/lipid typically used around 0.5–10% to reduce transepidermal water loss and improve barrier feel, and it is generally well-tolerated in sensitive and eczema-prone populations. Human repeat-insult patch testing and clinical use data show low irritation and low sensitization rates, with reactions being uncommon and more often related to impurities/oxidation rather than the molecule itself. Because rare irritation or comedogenic flares can still occur in highly reactive individuals, it is not fully inert, but it remains very gentle at typical cosmetic concentrations. Safety Notes: In commercial skincare, squalene is often used at very low levels (~0.05–0.5%) as part of the emollient/oil phase in cleansers, lotions, and creams where it contributes slip and barrier support without greasiness. Typical leave-on facial moisturizers and serums commonly fall around ~1–10%, while high-emollience balms/oils and “100% squalene” single-ingredient facial oils sold OTC reach the practical maximum of 100%. There is no specific EU/FDA cosmetic maximum for squalene; the main constraints are oxidation/stability and sensory profile, with leave-on products spanning the widest range.