Skincare Ingredients

Sodium Lauroyl Sarcosinate

Sodium lauroyl sarcosinate is an anionic surfactant/cleanser used commonly around 1–10% in rinse-off products, where it can disrupt the stratum corneum and increase transepidermal water loss, especially in eczema-prone or compromised skin. Patch testing and clinical experience show it is generally milder than SLS/SLES, but irritation and stinging are still plausible in sensitive individuals, particularly with frequent use, higher concentrations, or leave-on exposure. Given the predictable surfactant-related barrier irritation risk in reactive populations, a moderate score is warranted and patch testing is prudent for severely sensitive skin. Safety Notes: In commercial leave-on products (e.g., acne/blemish serums, lightweight emulsions) sodium lauroyl sarcosinate is sometimes used at very low levels (~0.1–1%) mainly as a solubilizer, wetting agent, or to aid sensory/cleansing in micellar-type formats. In rinse-off cleansers and shampoos it is commonly present around 2–12% as an anionic surfactant, while high-strength consumer-available cleansing concentrates and solid syndet-style bars can reach very high total surfactant loads where sarcosinate can be a primary surfactant at up to ~20–30% depending on actives basis and water content; higher levels are typically constrained by irritation potential and viscosity/salt curve behavior.

Sodium Laurylglucosides Hydroxypropylsulfonate

Sodium Laurylglucosides Hydroxypropylsulfonate is a mild anionic surfactant/cleansing agent typically used in rinse-off cleansers and shampoos (often a few percent active), generally less irritating than SLS but still capable of disrupting the stratum corneum barrier with repeated exposure. Patch-test and real-world use patterns show surfactants remain a common trigger for stinging, dryness, and eczema flares in highly reactive or compromised skin, especially with frequent washing or when combined with other detergents. For patient safety in severe sensitivity/eczema populations, I rate it as mild—usually tolerated, but not “exceptionally gentle” and not risk-free. Safety Notes: In commercial products, this mild anionic surfactant is most often used in rinse-off cleansers where total surfactant actives can vary widely; it appears at very low levels (~0.2–1%) as a secondary co-surfactant/foam booster in gentle facial cleansers and micellar/low-foam washes. At the high end, consumer-available high-foaming body washes, shampoos, and clarifying cleansers can use it as a primary surfactant system component, reaching roughly 10–20% active matter in concentrated or sulfate-free/high-foam formats. It is uncommon in true leave-on products beyond trace/low levels due to irritation potential and sensorial constraints, so the upper end is primarily observed in rinse-off formulations.

Sodium Lauryl Sulfate

Sodium Lauryl Sulfate is a strong anionic surfactant commonly used in cleansers and toothpastes (often ~0.5–10%) and is a well-established irritant in patch testing and controlled exposure studies, frequently causing barrier disruption, stinging, and eczematous flares. In sensitive, compromised, or atopic skin, even brief or repeated contact can provoke significant irritation due to its lipid/protein denaturing effects and cumulative damage with routine use. Given its consistent use as a positive control for irritation and the high likelihood of reactions in reactive populations, it warrants a very high irritancy score for patient safety. Safety Notes: In commercial skincare, SLS appears at very low levels (~0.05–0.5%) as a minor co-surfactant/foam booster in mild facial cleansers and some rinse-off washes, while many products avoid it entirely in leave-on formats due to irritation potential. Typical mass-market rinse-off cleansers, body washes, and shampoos commonly use ~1–15% SLS (often in blends with other surfactants). The highest consumer-available levels are seen in strong degreasing/clarifying cleansers and cleansing pastes/bars where SLS can reach roughly 20–30% as the primary anionic surfactant (still rinse-off; leave-on products are generally near zero to trace).

Sodium Levulinate

MVP Approved - Sodium Levulinate is a plant‐derived salt used in cosmetic formulations primarily for skin-conditioning and boosting preservative efficacy, and it contributes to hydration. It is generally mild and well-tolerated at typical usage levels.

Sodium Magnesium Fluorosilicate

Sodium magnesium fluorosilicate is an inorganic fluorosilicate salt more associated with industrial uses than leave-on skincare, and salts in this class can be irritating if they contact skin or mucosa, especially when dusted or present at meaningful levels. In sensitive or eczematous skin, ionic/fluoride-containing compounds can provoke stinging and barrier disruption, and safety data for routine cosmetic use are limited compared with standard cosmetic minerals. Given the uncertainty in cosmetic-grade exposure plus the potential for irritation in compromised skin, I score it as a significant irritant risk. Safety Notes: Sodium magnesium fluorosilicate is an uncommon cosmetic ingredient but is observed in a small number of consumer oral-care and occasional deodorant/antimicrobial-type rinse-off products as a fluoride/silicate salt, typically at trace-to-low levels (~0.01–0.2%) when used primarily for ancillary functional effects. Higher-strength OTC products that deliberately target fluoride delivery or stronger antimicrobial/deodorizing claims can reach about ~0.5–1.0%, with practical upper limits driven by taste/irritancy, solubility, and fluoride exposure considerations; it is rarely used in leave-on facial skincare at meaningful levels.

Sodium Metabisulfite

Sodium metabisulfite is a sulfite antioxidant/preservative that can provoke irritation and clinically relevant hypersensitivity reactions (including asthma-type responses and contact dermatitis) in susceptible individuals, even at the low concentrations typically used in formulations. Patch testing and case reports support that while not universally irritating, it is a higher-risk ingredient for reactive/eczema-prone patients, so I score it as significant to reflect the need for caution and patch testing. Safety Notes: In consumer skincare, sodium metabisulfite is most often used as an antioxidant/reducing agent and preservative adjunct at very low levels (commonly ~0.01–0.1%) in both leave-on and rinse-off formulas, with some products listing it near the end of the INCI at trace-to-low percentages. Higher consumer-available levels are observed in certain high-strength cleansing/hair-removal/bleaching-type cosmetic preparations and some rinse-off products where sulfite functionality is leveraged more aggressively, approaching ~0.5–1.0% while still remaining OTC (these higher levels are much less common in leave-on due to odor/sulfite sensitivity and irritation risk). Regulatory frameworks do not set a single universal cosmetic maximum for this ingredient, so practical market use is primarily constrained by sensitization labeling considerations, product odor, stability, and local compliance for sulfite-releasing substances.

Sodium Metaphosphate

Sodium metaphosphate is primarily used as a chelating/sequestrant and stabilizer in low concentrations, and it is not considered a classic irritant active like acids or retinoids. However, as an inorganic phosphate salt it can cause mild stinging or irritation on compromised barriers (e.g., eczema, post-procedure) at higher local exposure or in leave-on products, so it is best categorized as generally gentle but not completely inert. Given sensitive-skin safety considerations and limited robust human irritation datasets specific to this salt in cosmetics, a conservative 'gentle' score is appropriate. Safety Notes: Sodium metaphosphate (a polyphosphate chelating/sequestering salt) is most often used at very low levels (~0.01–0.3%) in mass-market cleansers, shampoos, soaps, and some emulsions to bind hard-water ions and improve stability/foam performance. In consumer-available specialty “water softener/chelant” or clarifying wash-type products (rinse-off) and some bath/cleansing concentrates, levels can be pushed into the low single digits, with the highest OTC examples observed around ~3–5% where solubility, ionic strength, and irritation/tackiness constraints typically become limiting (leave-on products rarely exceed ~0.5–1%).

Sodium Methyl Cocoyl Taurate

Sodium Methyl Cocoyl Taurate is a mild anionic surfactant commonly used in cleansers (often a few to ~15% in the surfactant blend) and is generally less irritating than traditional sulfates, with good skin and eye tolerability in rinse-off use. However, as a true detergent it can still disrupt barrier lipids and increase transepidermal water loss in eczema-prone or over-washed skin, so I rate it as gentle rather than very gentle for highly reactive patients. Safety Notes: In consumer products, Sodium Methyl Cocoyl Taurate is most often used in rinse-off cleansers as a mild primary or secondary surfactant; at the low end (~0.2–1%) it appears as a co-surfactant/foam booster or mildness modifier in sulfate-free face washes and body washes. Mid-range usage (~3–12%) is common for primary cleansing systems in gentle syndet-style gels/creams, while high-strength OTC formats (solid shampoo bars, syndet cleansing bars, and ultra-mild baby cleansers) can reach ~15–25% as part of the total surfactant blend (higher in solids, lower in liquids). Leave-on usage is uncommon and generally limited to trace/low levels when present.

Sodium Methyl Oleoyl Taurate

Sodium Methyl Oleoyl Taurate is a mild anionic surfactant commonly used in cleansers as a primary/secondary detergent (often a few percent in facial cleansers and higher in body washes), and it is generally well-tolerated compared with harsher sulfates. However, as a true cleansing surfactant it can still disrupt barrier lipids with frequent or prolonged contact, so stinging/tightness can occur in eczema-prone or highly reactive skin—especially in multi-surfactant, higher-foaming systems. Overall, clinical experience and patch-test data for taurate surfactants support a low but non-zero irritation risk, warranting a gentle (0.3) score rather than “very gentle” for compromised skin. Safety Notes: Sodium Methyl Oleoyl Taurate is a mild anionic surfactant primarily used in rinse-off cleansers; in commercial formulas it can appear at low levels (~0.2–2%) as a secondary co-surfactant/foam modifier in syndet blends. Typical consumer facial cleansers and body washes more often use it around ~3–12% (as supplied-active basis), while high-strength consumer-available solid syndet bars, cleansing pastes, and concentrated foaming cleansers can reach ~15–25% to build primary detergency and bar structure. Leave-on use is uncommon and generally stays at the low end due to irritation potential and the ingredient’s surfactant function.

Sodium Methyltaurate

Sodium methyltaurate is primarily used as a mild anionic surfactant/cleansing agent (often in the low single-digit % range up to ~10% in rinse-off formulas) and is generally better tolerated than harsher sulfates, but it can still disrupt barrier lipids and sting on compromised skin. Patch-test and consumer-use data typically place taurate surfactants in the low-irritancy category, yet eczema-prone and post-procedure patients can experience dryness or burning with repeated exposure, especially in multi-surfactant routines. Given its surfactant function and real-world cumulative cleansing exposure, I score it as gentle rather than “very gentle.” Safety Notes: In commercial skincare, sodium methyltaurate is most commonly used as an anionic co-surfactant/viscosity builder in mild facial cleansers and foaming products, where it can appear at very low levels (~0.05–0.3%) as a supporting surfactant or secondary thickener. Typical rinse-off cleansers are often ~1–4% depending on the total active surfactant system, while high-strength consumer-available cleansers and shampoo/body-wash type formulas using methyltaurate-based systems can reach ~6–8% (higher if expressed as total surfactant blend rather than this single component). It is generally used in rinse-off products far more than leave-on, where use levels tend to stay at the low end due to sensorial and surfactant-related irritation constraints rather than regulatory limits.

Sodium Myristoyl Sarcosinate

Sodium myristoyl sarcosinate is an anionic surfactant/cleansing agent typically used around ~1–10% in facial cleansers and foaming products, where irritation risk is driven by barrier lipid disruption and protein denaturation rather than true allergy. Human patch/usage experience with sarcosinate-based surfactants suggests they are often milder than classic sulfates, but they still produce stinging, dryness, and eczema flares in reactive or compromised skin—especially with frequent use or in multi-step routines that already include actives. Given the clinically meaningful risk in sensitive and atopic populations at functional cleansing concentrations, it warrants a “notable” score requiring careful selection and monitoring. Safety Notes: In commercial skincare, sodium myristoyl sarcosinate appears at very low levels (~0.05–0.3%) as a secondary mild surfactant/foam booster or solubilizing aid in leave-on emulsions and micellar-type systems, where higher levels would be too irritating or destabilizing. Most rinse-off facial cleansers and body washes use it in the low single digits (~1–6%) within multi-surfactant blends for mildness and foam quality. The highest consumer-available levels are seen in concentrated syndet/cleansing pastes, powder-to-foam cleansers, and high-foaming acne/oily-skin cleansers where it can reach ~10–15% active to deliver strong detergency, typically only suitable for rinse-off formats.

Sodium Palmate

Sodium palmate is a soap (sodium salt of palm fatty acids) used at high levels in bar cleansers, and its alkaline nature can disrupt the stratum corneum, increasing transepidermal water loss and provoking stinging, dryness, and eczema flares. Clinical experience and irritant contact dermatitis data for true soaps show moderate irritation potential, especially with frequent use or compromised barriers, so patch-testing and limited exposure are prudent for sensitive skin. Safety Notes: Sodium palmate is primarily used as the main soap surfactant/structurant in bar soaps and syndet-soap hybrid cleansing bars; in these rinse-off products it commonly appears at very high levels, with traditional “soap bars” and glycerin/transparent soap bases reaching roughly 60–85% of the finished bar as fatty acid sodium salts (including sodium palmate). At the low end, it shows up as a minor component or trace carryover (e.g., in cleansers or products containing soap noodles/soap base blends, or as an incidental impurity in certain fatty-acid–derived materials) around ~0.1–1%. It is rarely used in leave-on skincare at meaningful levels due to high alkalinity/irritation potential, so the practical market maximum is driven by rinse-off bar soap formats.

Sodium Palmitate

Sodium palmitate is the sodium salt of palmitic acid and a primary soap surfactant used at high levels in bar soaps; at its functional alkaline pH it can strip lipids and disrupt the stratum corneum, which is a common trigger for stinging, dryness, and eczema flares. While not a classic strong sensitizer, its irritancy in compromised or very sensitive skin is clinically relevant due to surfactant/pH effects and frequent, cumulative exposure (hand/body washing). For patient safety—especially in eczema-prone populations—this warrants a moderate irritancy score with patch testing/avoidance in flaring skin. Safety Notes: Sodium palmitate is most commonly encountered as a soap surfactant/structurant in rinse-off bar cleansers, where it can appear at very low levels (~0.1–2%) as a minor fatty-acid soap in syndet/hybrid cleansing bars or in formulas using small amounts of fatty-acid neutralization for structuring. At the high end, traditional soap bars and soap-based cleansing bars marketed to consumers can contain sodium palmitate as a primary component, with finished-product levels commonly in the ~40–80% range and specialty high-soap bars reaching roughly ~85% depending on water/glycerin/other soap salts content; it is uncommon in leave-on products except at trace/low levels due to alkalinity/irritation constraints.

Sodium Palmitoyl Sarcosinate

Sodium Palmitoyl Sarcosinate is an anionic surfactant/cleansing agent typically used around ~0.5–5% in rinse-off products, where it is generally milder than harsher sulfates but can still disrupt the stratum corneum and sting compromised skin. Patch/irritation testing for sarcosinate surfactants supports low-to-moderate irritation potential, with higher risk in eczema, barrier-impaired, or over-cleansed users and with cumulative exposure in multi-step routines. Given patient-safety considerations for highly reactive skin, I rate it as mild: usually tolerated but capable of provoking irritation in susceptible individuals. Safety Notes: Sodium palmitoyl sarcosinate is a mild anionic surfactant/foam booster most commonly found in rinse-off facial cleansers and body washes, where it can appear at low “supporting” levels (~0.05–0.5%) in blends to improve mildness and lather alongside other surfactants. In consumer-available high-foaming cleansers/shampoos and some acne/oily-skin washes, it can be used as a primary surfactant in the several-percent range, with upper-end commercial formulas reaching about 8–10% active to drive foam and detergency. Leave-on use is uncommon and typically kept at very low levels (generally ≤0.1–0.5%) due to irritation risk and surfactant sensorial constraints, so the market high end is driven by rinse-off products.

Sodium Palm Kernelate

Sodium Palm Kernelate is a soap (alkali salt of palm kernel fatty acids) used at high levels in bar soaps/cleansers, where it functions as a primary surfactant and typically creates an alkaline pH that increases barrier disruption. Clinically, soap-based surfactants are well-known to cause irritant contact dermatitis, especially in eczema-prone and compromised skin, with frequent dryness, stinging, and flare risk during routine use. Given its common use concentration and predictable cumulative irritation from repeated washing, it warrants a high irritancy score for sensitive populations. Safety Notes: Sodium palm kernelate is a primary anionic soap used almost exclusively in rinse-off cleansing formats; at the low end it appears as a minor component in syndet/combination bar formulas, liquid cleansers, or soap-based blends where it is listed but present at ~0.1–5%. At the high end, traditional true-soap bar products (e.g., palm/palm-kernel soap bars) can be predominantly soap, with sodium palm kernelate comprising roughly 50–85% of the finished bar depending on the fatty acid split and water/glycerin/salt levels. Leave-on products rarely use it due to high alkalinity/irritation potential; this range reflects consumer-available rinse-off products rather than professional-only materials.

Sodium PCA

MVP Approved - Sodium PCA is a naturally derived humectant widely used to boost skin hydration and soothe irritation, with a long history of safe use in cosmetic formulations.

Sodium PEG-7 Olive Oil Carboxylate

Sodium PEG-7 Olive Oil Carboxylate is a mild anionic surfactant/cleansing agent derived from olive oil and PEG, typically used at low-to-moderate levels in rinse-off cleansers to improve mildness and solubilization. While generally well-tolerated compared with harsher sulfates, surfactants can still disrupt barrier lipids and trigger stinging or eczema flares in highly reactive skin, especially with frequent use or in leave-on residues. Given its usual role and the known irritancy potential of cleansing agents as a class, it fits a “gentle” but not “very gentle” risk profile. Safety Notes: Sodium PEG-7 Olive Oil Carboxylate is used primarily as a mild anionic surfactant/solubilizer in rinse-off cleansing formats; in commercial products it is often present at low levels (~0.1–1%) as a co-surfactant/foam modifier or solubilizer in micellar waters, facial cleansers, and shower products. At the high end, specialty “sulfate-free” and oil-derived surfactant systems (cleansing gels, baby washes, intimate washes, and some shampoo/body wash concentrates) can use it as a primary surfactant or major component of the surfactant blend, reaching ~10–20% active in finished OTC products depending on the supplied raw material concentration. Leave-on use is comparatively uncommon and typically remains at the low end due to surfactant-related irritation potential, while rinse-off products account for the upper range.

Sodium Phosphate

Sodium phosphate is primarily a buffering/pH-adjusting and chelating salt typically used at low concentrations in leave-on and rinse-off products, where it is generally well tolerated and not a common cause of irritant contact dermatitis. However, because it can influence product pH and ionic strength (which can sting compromised or eczematous skin, especially near eyes or on fissured areas), it is not truly inert even though reactions are uncommon. In sensitive-skin populations, the realistic risk is low but nonzero, supporting a very gentle score rather than 0.0. Safety Notes: In cosmetics, sodium phosphate (typically mono-/di-/trisodium phosphate used singly or as part of phosphate buffer systems) is most often present at low levels (~0.05–0.5%) in leave-on lotions/serums and rinse-off cleansers to adjust and stabilize pH, chelate/assist stability, and support preservative performance. Higher-strength consumer products—especially exfoliating/clarifying masks, bath/cleansing powders, and some hair-color/bleach-related or high-alkalinity cleansing systems available retail—can use phosphate salts at ~1–3% to deliver stronger buffering/alkalinity control and formulation robustness; above this is uncommon in mainstream OTC skincare due to sensorial and pH/irritation constraints.

Sodium Phytate

MVP Approved - Sodium Phytate is primarily used as a chelating agent in cosmetic formulations to bind metal ions and stabilize products, and it is generally considered very mild on the skin.

Sodium Polyacrylate

Sodium polyacrylate is a high–molecular weight film-forming polymer/thickener used at low concentrations (typically well under a few percent) and is generally non-reactive on intact skin, with low rates of irritation in standard patch testing. However, in very compromised barriers (eczema, fissured or post-procedure skin), polymer films can occasionally cause stinging or friction/occlusion-related discomfort, so I cannot score it as fully inert. Overall it is very gentle for most sensitive users when formulated appropriately. Safety Notes: In commercial skincare, sodium polyacrylate is most often used as a rheology modifier/film former in leave-on lotions, sunscreens, and serums at low levels around 0.05–0.3%, and in rinse-off cleansers/body washes around ~0.1–0.5% to stabilize suspensions and improve feel. The highest consumer-available levels are seen in very thick gel-creams, hydrogel masks/patches, and “water gel” textures where sodium polyacrylate (sometimes alongside other acrylate thickeners) can reach ~1–5% total polymer to build viscosity and water-binding; above this becomes difficult to process/spread and is more typical of non-cosmetic absorbent applications. There is no specific EU/FDA maximum for sodium polyacrylate in cosmetics; practical use is limited by viscosity, tack, and salt/electrolyte sensitivity rather than regulation.

Sodium Polyacrylate Starch

Sodium Polyacrylate Starch is a superabsorbent polymer blend used primarily as a thickener/absorbent and film-former at low concentrations in leave-on and rinse-off products. Available patch-test and safety assessments for polyacrylate/starch-based rheology modifiers generally show low irritation potential, with reactions being uncommon and typically related to compromised barriers or formulation factors rather than the polymer itself. Given the very low intrinsic reactivity but acknowledging rare irritant responses in highly sensitized eczema patients (especially with occlusion), a 0.2 score best reflects typical clinical tolerability while staying cautious for severely reactive skin. Safety Notes: In commercial skincare, sodium polyacrylate starch (a superabsorbent polymer/thickener) is observed at very low levels (~0.05–0.3%) as a secondary rheology modifier/sensory powder in leave-on lotions/creams and some rinse-off cleansers. More commonly it sits around ~0.3–3% when used as a primary thickener/absorbent to build gel-cream textures and reduce tack in leave-on products. High-strength consumer products such as oil-control “dry touch” creams, balm-like leave-ons, and some waterless or high-solids texture products can reach ~5–8%, with higher levels typically limited by feel (powdery/drag), processing viscosity, and stability rather than specific regulatory caps.

Sodium Polyglutamate

Sodium polyglutamate is a film-forming humectant/skin-conditioning polymer typically used at low levels (about 0.1–2%) to improve hydration and feel, and it is generally well tolerated in patch testing with low rates of irritation. It is not pH-active and doesn’t have the barrier-disruptive behavior seen with acids, alcohols, or strong surfactants. Rare stinging can occur on severely compromised or post-procedure skin due to osmotic effects or formulation context, so I score it as very gentle rather than inert. Safety Notes: In commercial skincare, sodium polyglutamate is most often used as a humectant/skin-conditioning polymer at low levels (~0.01–0.3%) in both rinse-off cleansers and leave-on lotions/serums to boost hydration and improve feel. Higher levels are found in consumer-available high-hydration gel serums, sheet mask essences, and polymer-thickened “plumping” treatments where it can function as a primary moisturizing film former and viscosity builder (commonly ~0.5–2%), with the upper end around ~3% observed in specialty leave-on concentrates; above this, texture and tackiness typically become limiting.

Sodium Retinoyl Hyaluronate

Sodium Retinoyl Hyaluronate is a retinoid derivative (retinoyl group linked to hyaluronate) used as an anti-aging/renewal active, typically at low percentages but intended to deliver retinoid activity over time. Despite the hyaluronate carrier potentially improving tolerability, retinoid-class ingredients have well-documented risks of dryness, stinging, erythema, and barrier disruption—especially in eczema-prone or compromised skin and when layered with other actives. Given its functional intent as a retinoid and the cumulative irritation risk in real-world routines, it warrants an “active requiring careful introduction” score. Safety Notes: In real-world consumer skincare, sodium retinoyl hyaluronate (a retinoid–hyaluronic acid conjugate typically used for gentler, slow-release retinoid delivery) is commonly dosed at very low levels in leave-on serums/creams, with entry-level products frequently using ~0.0005–0.01% as a supporting anti-aging active. High-strength OTC specialty retinoid products marketed around this specific derivative have been observed up to about 0.1% in leave-on formats; higher levels are uncommon due to cost, color/odor and stability constraints, and irritation risk. It is rarely used in rinse-off products, where effective contact time is limited and practical use levels tend to remain at the low end of the range.

Sodium Rna

Sodium RNA (a nucleic-acid–derived skin-conditioning/humectant ingredient) is typically used at low concentrations and is not a keratolytic or pH-dependent active, so it generally has low inherent irritation potential. However, as a biologically derived macromolecule, it can still provoke stinging or rare hypersensitivity in highly reactive or barrier-compromised eczema skin, especially when layered with other actives. Given patient-safety considerations and limited robust irritancy datasets compared with core humectants, I score it as very gentle rather than exceptionally gentle. Safety Notes: In commercial skincare, Sodium RNA (often positioned as a “DNA/RNA” moisturizing/skin-conditioning active) is most commonly used at very low levels in leave-on serums/creams, with trace-to-low additions around 0.0001–0.01% reflecting typical supplier-recommended use levels and cost/stability constraints. Mid-range products (anti-aging lotions, eye creams, sheet masks) frequently sit around ~0.01–0.1%. The highest OTC consumer-available claims observed reach about 0.5–1.0% in specialized “nucleic acid” ampoules/serums, with >1% being uncommon due to solubility, tackiness/feel, and preservation/bioburden considerations rather than a specific regulatory cap.

Sodium Salicylate

Sodium salicylate is a salicylate salt used as a preservative/solubilizer and sometimes as a salicylic-acid derivative; at typical leave-on levels it is less keratolytic than salicylic acid but can still sting or irritate compromised skin. Clinical experience and patch-test data show salicylates can provoke irritant reactions in reactive or barrier-impaired patients and are a known concern for some with aspirin/salicylate intolerance. Given the potential for cumulative irritation in routines (especially alongside acids/retinoids) and the need for patch testing in eczema-prone skin, a moderate score is most patient-safe. Safety Notes: In commercial cosmetics, sodium salicylate is most often used as a low-level preservative booster/chelating-supporting adjunct or pH-dependent antimicrobial aid, with some leave-on and rinse-off products listing it around 0.01–0.1% alongside phenoxyethanol/organic acids. Higher levels are seen in consumer-available keratolytic/anti-blemish toners, lotions, and body products (and some anti-dandruff-style rinse-off products) where it functions as a salicylate exfoliant/salt form, typically 0.5–2% depending on pH and irritation tolerance. Above ~2% is uncommon in mainstream OTC skincare due to tolerability and because stronger salicylate exfoliation is generally delivered via salicylic acid rather than its sodium salt.

Sodium Silicate

Sodium silicate is a strongly alkaline inorganic salt (commonly used in detergents/industrial products and as a high-pH builder), and at functional concentrations it can significantly disrupt the skin barrier, causing stinging, irritant contact dermatitis, and even chemical-burn–type reactions on compromised skin. While trace amounts in a well-buffered cosmetic would lower risk, its typical utility is pH elevation/alkalinity, which is inherently incompatible with eczema-prone or sensitized skin. Given its caustic potential and the severe outcomes seen with high-pH exposures, it warrants a very high irritancy score for patient safety. Safety Notes: In consumer skincare, sodium silicate is most often encountered at trace-to-low levels as an alkalinity/pH adjuster or processing aid in rinse-off cleansers, soaps, and some exfoliating masks, with commercial use commonly starting around ~0.05–0.2%. The highest OTC levels are seen in strongly alkaline, rinse-off cleansing/purifying products (e.g., certain deep-clean masks/soaps and specialty high-pH cleansers) where it can reach ~3–5% active sodium silicate; higher levels are generally constrained by high pH, irritation/corrosivity concerns, and destabilization of many cosmetic systems, making leave-on usage typically ≤0.5% and rare at the upper end.

Sodium Stearate

Sodium stearate is a soap surfactant/emulsifier commonly used in cleansing bars and some creams, and as an anionic surfactant it can disrupt the stratum corneum and increase dryness/irritation—especially in leave-on or high-foaming products and when combined with other detergents. While not a frequent true allergen, clinical experience and patch/usage data show it can sting or flare eczema in reactive individuals due to its detergent action and the typically higher pH environment in soap-based formulas. Given real-world cumulative exposure in routines and the heightened risk for compromised barriers, I rate it as mild irritancy rather than “gentle.” Safety Notes: In mainstream skincare, sodium stearate is most often encountered at very low levels (≈0.05–1%) as a stabilizing fatty-acid soap/emulsifier or as a gellant/structurant in creams, cleansing creams, and some deodorant-style sticks. The highest consumer-available levels are found in rinse-off cleansing bars and soap-based facial/body cleansing bars, where sodium stearate (formed from stearic acid neutralization or added directly) commonly reaches ~10–25% of the finished bar to build the primary surfactant/structure system. It is uncommon in high percentages in leave-on lotions/creams due to alkalinity/soap feel and compatibility constraints, so the upper end of the observed market range is driven by rinse-off bar formats.

Sodium Stearoyl Glutamate

Sodium stearoyl glutamate is an amino‑acid–derived surfactant/emulsifier typically used at low concentrations (about 0.1–3%) to stabilize creams and provide mild cleansing/emulsifying without strong lipid stripping. Human experience and patch-test data generally show low irritation potential compared with harsher anionic surfactants, though any surfactant can sting or irritate very compromised skin (eczema flares, post-procedure) especially in leave-on products layered with other actives. Given its generally good tolerability but nonzero surfactant-related risk in highly reactive patients, it fits best as very gentle rather than inert. Safety Notes: Sodium stearoyl glutamate is an amino-acid–derived emulsifier/co-emulsifier and mild anionic surfactant typically used at low levels (~0.05–0.3%) in leave-on creams/lotions to stabilize oil-in-water emulsions and improve skin feel, and around ~0.5–2% in cleansers and lotion-like emulsions where it also contributes to cleansing/foam. In consumer-available high-structure emulsions, balm-to-milk cleansers, and “natural”/PEG-free emulsifier systems, it is observed up to about 3–5% as a primary emulsifier/surfactant blend component; higher levels are uncommon due to viscosity/lamellar-structure constraints and potential irritation/soaping in leave-on formats.

Sodium Stearoyl Lactylate

Sodium stearoyl lactylate is an emulsifier/surfactant typically used at low concentrations (about 0.1–2%) to stabilize formulations and improve skin feel. Available safety and patch-test data generally show low irritation and low sensitization potential, though as a surfactant-type ingredient it can occasionally sting or irritate very compromised barriers (e.g., active eczema or post-procedure skin). Given its usual low use level and overall good tolerability but non-zero risk in highly reactive patients, it fits a "very gentle" score. Safety Notes: In consumer skincare, sodium stearoyl lactylate is most often used as a co-emulsifier/lamellar structurant at low levels (~0.05–0.3%) in light lotions, facial moisturizers, and cleansers where it supports stability and skin feel without materially impacting viscosity. Mainstream leave-on creams and body lotions commonly sit around ~0.5–2% as part of the primary emulsifier system. The upper end (~3–6%) is seen in high-structure, wax-free or “barrier/repair” style creams and some solid/anhydrous-to-water systems where formulators push lamellar gel network formation and stability; higher levels are limited by tack/soaping and sensory constraints rather than specific cosmetic regulatory caps.

Sodium Succinate

Sodium succinate is a salt of succinic acid primarily used as a buffering/humectant-support ingredient, typically at low concentrations, and it is not generally associated with meaningful irritation in patch-testing or routine cosmetic use. While salts can occasionally sting on severely compromised skin (e.g., acute eczema flares or post-procedure barrier disruption), the overall clinical irritancy potential is low compared with true actives or acids at functional pH. For patient safety in highly reactive populations, I score it as very gentle rather than inert. Safety Notes: Sodium succinate is most often used as a minor buffering/skin-conditioning component or part of preservative/chelating/fragrance-adjacent systems, where commercial leave-on and rinse-off products commonly include it at trace to low levels around 0.001–0.1%. Higher concentrations are seen in consumer-available “succinate” or multi-salt buffering/mineral/ferment-style formulas and some masks/cleansers where it can function more meaningfully as a pH-modifier/osmolyte, reaching about 0.5–2% without entering prescription/professional-only territory. There is no specific FDA/EU maximum for sodium succinate in cosmetics; practical upper limits are driven by ionic strength, sensory (saltiness/tack), and pH/buffering targets rather than regulation.