Skincare Ingredients

Bromelain

Bromelain is a proteolytic enzyme used for enzymatic exfoliation/anti-inflammatory effects, typically around ~0.1–2% in leave-on or rinse-off products, and its protease activity can disrupt a compromised stratum corneum and cause stinging, erythema, or dermatitis in sensitive users. Clinical experience and patch testing reports for proteolytic enzymes support a meaningful irritation potential, particularly on eczema-prone or barrier-impaired skin and when layered with other exfoliants or retinoids. Given the risk of both irritant reactions and possible allergy in susceptible individuals, it should be introduced cautiously and patch tested. Safety Notes: In commercial OTC skincare, bromelain is most often used at very low levels (~0.01–0.1%) in enzyme cleansers and gentle exfoliating masks/peels, largely due to irritation risk and the need to control proteolytic activity. Higher-strength consumer-available exfoliating powders, wash-off masks, and peel-like products can reach ~1–5% bromelain (often alongside papain/other enzymes), with wash-off formats dominating the upper end because they better manage skin tolerability and enzyme stability. There is no specific FDA/EU maximum for bromelain as a cosmetic ingredient, so observed limits are primarily practical (stability, odor/color, and irritation).

Buddleja Davidii Extract

Buddleja Davidii Extract is a botanical antioxidant/soothing extract typically used at low concentrations in cosmetic formulas, and it is not considered a potent exfoliant or barrier-disrupting active. However, as with many plant extracts, there is a non-zero risk of irritant or allergic contact dermatitis in sensitized or highly reactive individuals, especially in compromised skin. In sensitive-skin safety terms, it is generally well tolerated but not truly inert, supporting a gentle (0.3) score. Safety Notes: In commercial skincare, Buddleja davidii extract is commonly used as a botanical antioxidant/anti-pollution adjunct in leave-on products, where it often appears at very low levels (~0.001–0.05%) due to being supplied as a dilute extract blend and used primarily for claims support. More performance-driven serums/day creams and sunscreen-adjacent “blue light/urban defense” products typically formulate the active extract around ~0.1–1%, with the highest OTC consumer products observed reaching about 2% when the extract is the primary featured botanical and the supplier system supports stability and aesthetics. Rinse-off products generally sit toward the low end because short contact time reduces the need for higher dosing.

Buddleja Officinalis Flower Extract

Buddleja officinalis flower extract is a botanical antioxidant/soothing extract typically used at low concentrations, but like many plant extracts it contains multiple bioactive compounds that can trigger irritation or allergic contact dermatitis in reactive or eczema-prone skin. Robust clinical patch-test data specifically isolating this extract is limited, so for patient safety I score it as mild: generally tolerated but with a non-trivial risk of sensitivity, especially in compromised skin or multi-ingredient routines. Safety Notes: In mass-market leave-on skincare (SPF, day creams, anti-pollution/blue-light serums), Buddleja officinalis flower extract is typically used as a minor antioxidant/photoprotective support at trace-to-low levels (often via blends), with commercial formulas commonly landing around 0.01–0.5%. Specialty “urban defense/blue-light” products and concentrated botanical serums sometimes dose the extract much higher, with observed OTC maxima around ~2–3% depending on extract potency/solvent system and sensory constraints. Rinse-off cleansers generally sit toward the low end due to short contact time and cost/clarity limits, while leave-on products span the full range.

Bumetrizole

Bumetrizole is an oil-soluble UV filter/photostabilizer used in sunscreens at low-to-moderate concentrations, and available data generally show low rates of irritation and sensitization in standard patch testing. However, as a chemical UV filter it is not completely inert—stinging or dermatitis can occur in highly reactive or eczematous skin, especially with compromised barriers and leave-on exposure. For patient-safety prioritization in sensitive populations, this fits a "gentle" but not "very gentle" irritancy profile. Safety Notes: Bumetrizole (UV filter/photostabilizer; commonly listed as Bumetrizole or Butyl Methoxydibenzoylmethane stabilizer in some markets) is observed in commercial leave-on sunscreens and day creams at low levels around ~0.1–1% when used primarily as a stabilizer/auxiliary UV absorber. High-strength consumer sunscreens, particularly in markets allowing higher UV-filter loads, have been marketed with bumetrizole in the mid-to-high single digits, with up to ~10% appearing in some OTC leave-on sunscreen formulations; it is uncommon in rinse-off products.

Bupleurum Falcatum Root Extract

Bupleurum falcatum root extract is a botanical anti-inflammatory/soothing extract used at low levels (typically <1–2%) in cosmetics, but like many plant extracts it contains multiple bioactive constituents (e.g., saponins/flavonoids) that can provoke stinging or contact dermatitis in a reactive subset. Human patch-test and clinical irritation data are limited and not robust enough to classify it as reliably “very gentle” for compromised skin. Given the uncertainty and the known higher sensitization risk category of botanicals, a mild irritation score is the safest clinically aligned choice. Safety Notes: In commercial skincare, Bupleurum falcatum root extract is most often used as a soothing/anti-redness botanical in leave-on toners/serums/creams at very low levels (often ~0.001–0.1%) because it is typically supplied as a dilute glycerin/butanediol/water extract and is used as part of a multi-extract blend. Higher-strength consumer products (mostly K-beauty/J-beauty “herbal” ampoules/essences or minimalist botanical-focused serums) can reach ~1–5% when the extract is a standardized, low-odor liquid or powder reconstituted into the formula; above this becomes uncommon due to color/odor, potential tackiness, and stability/compatibility constraints rather than regulatory limits. Rinse-off products generally sit at the lower end (≈0.001–0.5%) since contact time is short and botanical loads are often minimized for cost and sensory reasons.

Butyl Acetate

Butyl acetate is a volatile solvent/fragrance component primarily used to dissolve other ingredients and impart scent; when present (often in low percentages) it can still defat the stratum corneum and sting compromised skin. Human exposure data and safety reviews consistently flag eye and mucous-membrane irritation and potential skin irritation from solvent contact, with risk amplified in eczema or barrier-impaired patients and with repeated use in leave-on products. Given its solvent nature, volatility, and higher likelihood of triggering irritation in sensitive populations even at typical cosmetic levels, it warrants a significant irritancy score. Safety Notes: In skincare-adjacent consumer products, butyl acetate is most often used as a minor fragrance/solvent trace in leave-on products (creams, lotions, perfumes/body mists), where finished-product levels can be in the low ppm range (~0.0005–0.05%) depending on the fragrance load. The highest OTC consumer-available levels occur in solvent-dominant systems such as nail polish/top coat and some nail polish removers/brush cleaners, where butyl acetate can be a primary solvent commonly spanning ~20–80% (sometimes higher in niche products), which sets the upper end of the observed market range. There is no specific EU/FDA cosmetic maximum for butyl acetate, so practical use is driven mainly by product type, odor/irritation tolerance, and flammability/volatile solvent handling rather than a hard regulatory cap.

Butylene Glycol

MVP Approved - Butylene Glycol is a commonly used humectant and solvent that improves hydration and product texture while exhibiting very low irritancy in standard cosmetic formulations.

Butyl Methoxydibenzoylmethane

Butyl methoxydibenzoylmethane (avobenzone) is a UVA filter typically used around 2–3% in sunscreens and is generally well-tolerated, but it has documented potential to sting or irritate, especially on compromised skin or near the eyes. Patch-test data suggest irritant reactions are uncommon but do occur, and true allergy is rare yet possible. Given real-world cumulative exposure (daily application, reapplication, and combinations with other UV filters/solvents), I rate it as mild irritancy risk for sensitive and eczematous patients. Safety Notes: Butyl Methoxydibenzoylmethane (avobenzone) is an oil-soluble UVA filter used almost exclusively in leave-on sun care and daily moisturizers with SPF; at the low end, it appears around ~0.1–1% in lower-SPF or combination-filter formulas where it is supported by other UVA/UVB filters. High-strength OTC sunscreens in the US commonly use avobenzone at 2–3%, and the highest consumer-available products reach 5% (the FDA monograph maximum for avobenzone in OTC drug sunscreens), typically requiring photostabilizers (e.g., octocrylene) and appropriate solvent/emollient systems.

Butyloctanol

Butyloctanol is a fatty alcohol/emollient and solvent used in leave-on products typically around ~1–10% to improve slip and reduce tack; it is not an exfoliating or pH-dependent active. Available safety and patch-test experience generally show low irritation potential, with reactions being uncommon and usually limited to highly reactive or barrier-compromised individuals when combined with other irritants. Given its generally good tolerability but non-zero chance of irritation in severe sensitivities, it fits best as very gentle rather than fully inert. Safety Notes: Butyloctanol is used in consumer skincare as an emollient, slip agent, and solvent for lipophilic actives/fragrance, and it often appears at low levels (~0.1–1%) in leave-on serums, lotions, and sunscreens to improve sensorial feel and aid solubilization. In richer leave-on creams, balms, cleansing oils, and makeup-adjacent skincare, it is commonly used in the mid-range (2–10%) as part of the emollient blend. High-emollient anhydrous sticks/balms and some cleansing oil/balm formats available OTC can reach ~20–30% when butyloctanol is a primary emollient; there is no specific EU/FDA maximum concentration limit for butyloctanol beyond general cosmetic safety requirements.

Butyloctyl Salicylate

Butyloctyl Salicylate is a non-exfoliating salicylate ester used mainly as an emollient/solvent and UV-filter booster, typically at a few percent up to ~10% in sunscreens and cosmetics. As an ester it lacks the keratolytic acidity of salicylic acid and is generally well tolerated, but salicylate-derived materials can still trigger stinging or rare contact reactions in highly reactive or eczema-prone skin—especially in leave-on, occlusive routines—so it is best classified as gentle rather than exceptionally gentle. Safety Notes: Butyloctyl Salicylate is used as an emollient/solubilizer and UV filter “booster” (oil-phase solvent) and appears at low levels (~0.1–1%) in many leave-on moisturizers and sunscreens as part of the emollient system or to help solubilize UV filters. In higher-performance OTC sunscreens and some anhydrous/tinted SPF products, it can be a major part of the oil phase, with commercial formulas using roughly 10–30% to improve feel, spread, and UV filter compatibility; rinse-off products typically use it at the low end due to cost/need and wash-off nature.

Butylparaben

Butylparaben is a preservative typically used at low concentrations (generally well under 1%), and controlled data suggest it has low primary irritancy for most users. However, parabens can trigger allergic contact dermatitis in a small but clinically meaningful subset—especially in eczema or barrier-impaired patients—so I rate it as mild rather than gentle to reflect that occasional sensitivity is possible. Safety Notes: In modern OTC cosmetics where butylparaben is still used, it most often appears as part of a parabens blend, with butylparaben at very low “supporting” levels (about 0.001–0.02%) in leave-on creams/lotions and some rinse-off cleansers. High-strength consumer-available products (especially older-style or region-specific body creams, hair products, and some makeup/skincare preserving systems) have used butylparaben up to the EU single-paraben cap of 0.14% (as acid) in finished products, which effectively defines the observed upper end for legitimate commercial formulas. The U.S. does not set a specific maximum, but mainstream formulations typically stay within EU-aligned limits for global compliance.

Butylphenyl Methylpropional

Butylphenyl Methylpropional (Lilial) is a fragrance ingredient used at low concentrations, but fragrances are among the most common triggers of irritant and allergic contact dermatitis, especially in eczema-prone skin. Patch-test data and real-world dermatology experience show meaningful sensitization risk despite “small amounts,” and it can amplify cumulative irritation when layered with other fragranced products. Given the high patient-safety stakes in compromised skin, it warrants a significant irritancy score. Safety Notes: Butylphenyl Methylpropional (Lilial) is prohibited for use in cosmetic products in the EU/UK and has been broadly removed from mainstream OTC skincare globally; current consumer products are therefore effectively formulated at 0%. While historically it appeared as a fragrance component at trace-to-low levels in both leave-on and rinse-off products, it is no longer considered an acceptable market-available cosmetic ingredient in compliant consumer skincare, so the observed present-day range is 0%.

Butyrospermum Parkii Butter

Rich, nourishing natural butter

Butyrospermum Parkii Butter Extract

Butyrospermum Parkii (shea) butter extract is primarily an emollient/skin-conditioning ingredient, typically used at low-to-moderate levels and generally well-tolerated even in dry or eczema-prone skin. However, as a botanical lipid extract it contains minor unsaponifiables that can occasionally trigger irritation or contact allergy in highly reactive individuals, especially on compromised skin or when oxidized/impure. Given the low overall irritancy but non-zero sensitization potential, a gentle-but-not-inert score is most consistent with patient safety. Safety Notes: In commercial skincare, Butyrospermum Parkii (Shea) Butter Extract is most often used as a minor emollient/skin-conditioning botanical at very low levels (about 0.01–0.1%) in lotions, facial creams, and cleansers where it supports marketing claims without materially affecting texture. Higher-strength consumer products (rich body butters, barrier balms, and some lip care) can use the extract form around 1–5% to boost conditioning and claim substantiation, while formulas aiming for very high “shea” content typically use shea butter itself rather than the extract. This range applies mainly to leave-on products; rinse-off products generally sit toward the lower end due to wash-off and cost/benefit.

C10-30 Cholesterol/Lanosterol Esters

C10-30 Cholesterol/Lanosterol Esters are lipid esters used primarily as emollients/texture agents, typically included at low-to-moderate percentages to improve barrier feel and reduce TEWL. As non-volatile, non-acidic, non-surfactant lipids, they are generally well-tolerated in patch testing and are more likely to be soothing than stinging, with irritation mainly limited to rare individual sensitivity or formulation-related factors (e.g., occlusive overload in very reactive skin). Given the strong overall tolerability profile but non-zero risk in highly sensitized eczema populations, they fit best as “very gentle” rather than fully inert. Safety Notes: In commercial skincare, C10-30 Cholesterol/Lanosterol Esters are most often used as a lipidic emollient/structuring agent in O/W creams and lotions, where it can appear at trace functional levels (~0.05–0.2%) to tweak feel and barrier-lipid profiles. Many mainstream leave-on moisturizers and barrier creams sit around ~0.5–3% for meaningful sensory and lamellar-structure support, while high-lipid balms, cold creams, and rich barrier-repair products available OTC can reach ~5–10% in the total formula to maximize occlusivity and cushion without being prescription-only. Rinse-off products tend to use the lower end due to wash-off and cost/phase-balance constraints, with the upper end primarily observed in leave-on, anhydrous or very oil-rich systems.

C11-15 Pareth-7

C11-15 Pareth-7 is a nonionic ethoxylated surfactant/solubilizer used in cleansers and emulsions (often ~0.5–5%+, higher in rinse-off systems), and surfactants are a common cause of barrier disruption and stinging in eczema-prone skin. While generally considered milder than anionic detergents, clinical experience and patch testing show occasional irritant reactions, especially with compromised skin or leave-on exposure. Given its surfactant role and cumulative irritation potential in routines, I rate it as mild rather than gentle for sensitive populations. Safety Notes: C11-15 Pareth-7 is a nonionic surfactant/solubilizer used at very low levels (~0.05–0.5%) in leave-on lotions/serums and facial moisturizers mainly to aid solubilization and improve spreading, and more commonly around 1–5% in rinse-off cleansers and micellar/cleansing products as part of the surfactant system. In high-strength consumer-available products such as concentrated makeup removers, cleansing oils/balms that rely on ethoxylated nonionics for self-emulsification, and some concentrated body washes, total usage can reach ~10–20% as a primary surfactant/emulsifier; higher levels are constrained by irritation potential and formula aesthetics rather than a specific global regulatory maximum.

C12-15 Alkyl Benzoate

MVP Approved - C12-15 Alkyl Benzoate is a lightweight emollient used in skincare formulations to enhance hydration and improve product texture while maintaining a low irritation profile.

C12-18 Acid Triglyceride

C12-18 Acid Triglyceride is an emollient lipid (medium/long-chain fatty acid triglycerides) typically used at a few percent up to higher levels to improve slip and barrier feel; it is not a pH-dependent active and has low inherent reactivity. Clinical experience and patch-test data for similar triglyceride emollients show a very low rate of irritation, though a small subset of highly reactive or compromised-skin patients can still experience stinging or contact reactions to any lipid vehicle or impurities. Given its generally excellent tolerability but non-zero risk in severe sensitivity populations, it fits 'very gentle' rather than completely inert. Safety Notes: C12-18 Acid Triglyceride (a medium-to-long-chain triglyceride emollient) appears at low levels (~0.1–1%) as a slip agent/emollient adjunct in lotions, serums, and facial cleansers, especially where it supports sensory feel without materially changing the oil phase. In leave-on creams, balms, and body butters it is commonly used as a primary emollient/oil-phase component and can reach ~20–60% in anhydrous or near-anhydrous consumer products (balms, ointment-style moisturizers, cleansing balms), with rinse-off formats typically lower due to surfactant system limits. No specific EU/FDA maximum restriction is generally applied to this type of triglyceride; practical upper limits are driven by texture, stability, and packaging.

C13-14 Isoparaffin

C13-14 Isoparaffin is an inert, mineral-oil–derived emollient/solvent used in leave-on products (often a few to ~10%+) to improve slip and reduce transepidermal water loss, and it is generally non-stinging and well tolerated in sensitive and eczema-prone skin. Clinical experience and patch-test data support a low rate of true irritation or allergy, but in highly reactive individuals its occlusive nature and formulation context (e.g., surfactants, preservatives) can still contribute to occasional discomfort or follicular issues, so it is best scored as very gentle rather than completely inert. Safety Notes: C13-14 Isoparaffin is most often used as the oil-phase carrier in gel-cream textures (commonly paired with Laureth-7) and appears at low levels (~0.1–1%) in emulsions/cleansers mainly as a slip/solvent aid or as part of a pre-blended thickening system. In leave-on gel creams and some primers, commercial formulas commonly use it in the mid-single to low-double digits, and the highest consumer-available products observed (very anhydrous/gelled hydrocarbon bases or high-slip makeup/skin primers) can reach ~20–25% without being prescription or professional-only. Rinse-off products generally sit toward the lower end due to surfactant dilution and cost/feel targets, while leave-on texture gels drive the upper end.

C13-15 Alkane

C13-15 Alkane is a lightweight emollient/hydrocarbon solvent used at relatively high levels in moisturizers and makeup to improve slip and reduce transepidermal water loss. Clinically it is generally well-tolerated and considered non-sensitizing, but in highly compromised barriers (eczema, post-procedure) any solvent-like emollient can occasionally sting or feel irritating, so it is not truly inert. Given the very low but non-zero irritation potential in reactive patients, it fits best as exceptionally gentle rather than 0.0. Safety Notes: In commercial products, C13-15 Alkane is often used at low levels (~0.1–2%) as a slip agent/emollient in lotions, serums, sunscreens, and makeup where it supplements other emollients and improves sensory. Mid-to-high levels (5–30%) are common in anhydrous balms, primers, and silicone-free creams where it functions as a major emollient/solvent. The highest consumer-available levels (50–95%) occur in essentially anhydrous “face oils,” cleansing oils, and minimalist emollient concentrates where C13-15 Alkane serves as the primary carrier; it is used mainly in leave-on and oil-based rinse-off formats, with no specific FDA/EU maximum concentration limit when used as a cosmetic ingredient under standard safety substantiation.

C14-22 Alcohols

C14-22 Alcohols are long-chain (fatty) alcohols used primarily as emollients, thickeners, and stabilizers, typically at low-to-moderate concentrations in creams/lotions, and they are generally well-tolerated compared with short-chain “drying” alcohols. Clinical experience and patch-test data indicate a low rate of irritation or allergy, but compromised barrier skin (e.g., active eczema) can react to almost any structuring agent, so they are not fully inert. Given the very low but non-zero irritation potential in highly reactive patients, a very gentle score is most consistent with safety-focused assessment. Safety Notes: C14-22 Alcohols (a fatty alcohol blend) is commonly used at very low levels (~0.1–0.5%) as an emulsion stabilizer/viscosity aid in lotions, cleansers, and serums where it appears mid-to-late INCI. In richer leave-on creams, body butters, and some hair/skin conditioning emulsions, it is used more structurally as part of the fatty phase, with commercial products commonly reaching ~3–8% and high-structure OTC formulations observed up to about 10%. This ingredient is not independently restricted by major cosmetic regulations, so the practical upper end is driven by aesthetics, waxiness, and emulsion stability rather than regulatory limits.

C15-19 Alkane

C15-19 Alkane is a lightweight emollient/hydrocarbon solvent (often used as an isododecane alternative) typically included at several percent up to higher levels to improve slip and reduce greasiness. In clinical use it is generally non-sensitizing and has very low irritancy potential because it is nonpolar, nonreactive, and does not alter skin pH; reactions are uncommon and usually relate to overall formula effects (occlusion, friction) rather than the ingredient itself. Given its excellent tolerance even in compromised barriers but acknowledging rare individual reactivity, it fits an exceptionally gentle score rather than completely inert. Safety Notes: C15-19 Alkane (a light emollient/hydrocarbon often used as a volatile-like silicone alternative) appears at low levels (~0.1–1%) in emulsions and cleansers primarily for slip, spreadability, and sensory optimization. In leave-on oils, oil-serums, silicone-free primers, and anhydrous balm-to-oil textures it can serve as a principal carrier/emollient, commonly 10–40% and reaching ~60–70% in high-slip, fast-dry consumer-available anhydrous formulas. It is generally not subject to a specific EU/FDA concentration cap for cosmetics, so the upper end is driven mainly by product format, stability, and sensorial targets rather than regulation.

C18-36 Acid Triglyceride

C18-36 Acid Triglyceride is a high–molecular weight lipid emollient/structuring agent used at low to moderate concentrations to improve texture and reduce transepidermal water loss. As a non-volatile, non-reactive triglyceride mixture, it is not an active and is generally well tolerated in patch testing with irritation being uncommon. In very reactive or eczema-prone patients, any rich lipid can rarely contribute to subjective stinging or follicular issues, so I do not score it as fully inert but still very gentle. Safety Notes: C18-36 Acid Triglyceride is commonly used as a viscosity builder/structurant and emollient in leave-on creams, lotions, and stick/balm formats, where it often appears at low levels (~0.1–1%) as a secondary thickener or sensory modifier. In richer anhydrous balms, pomades, and high-structure body butters (OTC consumer products), it can be a primary structuring lipid and is observed in the ~10–20% range to build firmness, payoff, and gloss. Rinse-off cleansers typically sit toward the low end (if used at all) due to surfactant dilution and cost/handling, while the highest levels are predominantly in leave-on anhydrous or low-water systems.

C18-38 Alkyl Hydroxystearoyl Stearate

C18-38 Alkyl Hydroxystearoyl Stearate is a high–molecular weight emollient/structuring wax ester used to improve slip, film formation, and texture, typically at low-to-moderate percentages in leave-on products. As a non-volatile, non-reactive lipid-like material, it has a low likelihood of causing stinging or barrier disruption and is generally well tolerated in patch testing, though very reactive eczema patients can still rarely flare to any occlusive emollient. Given its largely inert profile but acknowledging occasional sensitivity in compromised skin, it fits best as very gentle rather than completely inert. Safety Notes: C18-38 Alkyl Hydroxystearoyl Stearate is used as a structuring, slip/feel modifier and oil-phase gellant in leave-on creams, lotions, sunscreens and color cosmetics; in real-world INCI lists it can appear at very low levels (~0.05–0.3%) as a secondary texture aid. Typical usage for sensory/viscosity building is ~0.5–5%, while high-structure consumer products (balms, sticks, anhydrous pomades, heavy barrier creams) can reach ~10–15% to achieve firm gel networks and pay-off; rinse-off formats generally sit toward the low end because less structuring is needed.

C20-40 Pareth-40

C20-40 Pareth-40 is a polyethylene glycol ether surfactant/solubilizer used at low-to-moderate levels to emulsify and stabilize formulas; as a nonionic ethoxylated surfactant it is generally well tolerated but not inert. Patch-test data and clinical experience indicate occasional irritant reactions can occur in very reactive or barrier-impaired skin (especially if used in higher surfactant loads or left-on products), but it is typically less irritating than anionic surfactants, supporting a gentle (0.3) score. Safety Notes: C20-40 Pareth-40 is a high-HLB nonionic surfactant/solubilizer and emulsifier (commonly used with fatty alcohols or in gel-cream systems) that appears at very low levels (~0.05–0.3%) in leave-on lotions/serums mainly as a solubilizer or emulsion stabilizer. In richer O/W creams, cleansing creams, and some makeup-remover/balm-to-milk or heavy-duty solubilizing systems available OTC, it is used more materially as a primary emulsifier/solubilizer typically in the 1–5% range, with observed high-strength consumer formulations reaching ~6–8% to keep high oil loads/fragrance or complex actives solubilized and stable. This ingredient is not subject to a specific EU/FDA maximum for cosmetics, so practical stability/sensory limits rather than regulation usually cap the upper end.

C9-12 Alkane

C9-12 Alkane is a lightweight emollient/solvent (often used as an isododecane-like hydrocarbon) typically included at a few percent up to higher levels in makeup and leave-on formulations to improve slip and reduce greasiness. As a nonpolar, nonreactive hydrocarbon, it has very low inherent irritancy in patch testing and clinical use, with reactions being uncommon and more often related to overall formula factors (occlusion, co-ingredients, or impaired barrier) rather than the alkane itself. Given the need to protect highly reactive/compromised skin while acknowledging rare intolerance, it fits best as exceptionally gentle rather than completely inert. Safety Notes: In commercial products, C9-12 Alkane commonly appears at low levels (~0.1–2%) as a slip/feel modifier or light emollient in emulsions (e.g., lotions, sunscreens, serums), including both leave-on and rinse-off formats. At the high end, it is sold OTC as the primary/near-neat base in anhydrous facial oils, makeup primers, and silicone-free “dry oil”/emollient concentrates where it can comprise the bulk of the formula (often 60–95% and occasionally approaching ~99% in very minimal-ingredient blends). There is no specific FDA/EU concentration cap for this cosmetic emollient; practical limits are driven by product form (emulsion vs anhydrous) and desired sensorial properties.

Caesalpinia Spinosa Gum

Caesalpinia Spinosa Gum (tara gum) is a polysaccharide thickener/film-former used at low concentrations (typically ~0.1–1%) to stabilize and texture products, and it is generally non-reactive on skin. Clinical experience and patch-test data for similar botanical gums suggest a low but non-zero risk of irritation or contact allergy from plant-derived impurities/proteins, especially in eczema-prone or highly reactive patients. Because it is not an active and is usually used at low levels, I rate it very gentle but not fully inert. Safety Notes: Caesalpinia Spinosa Gum (tara gum) is used as a rheology modifier/film former; in commercial leave-on lotions, serums, and masks it commonly appears at low structuring levels around 0.05–0.3% (often in combination with other gums/thickeners). Higher-strength consumer products such as thick gel masks, peel-off style masks, and some “natural” high-viscosity creams can use roughly 1–3% to build body and film, with ~3% representing the upper end observed before texture (stringiness/tack) and processing constraints typically become limiting; rinse-off products tend to sit in the same or slightly higher band when a very viscous texture is desired.

Caffeic Acid

Caffeic acid is a phenolic acid antioxidant used in low concentrations in topical products, but as an acidic, bioactive polyphenol it can sting and provoke irritant dermatitis in compromised barriers (e.g., eczema), especially in leave-on formulas and when layered with other acids/retinoids. Patch testing and clinical experience with phenolic/plant-derived acids show a non-trivial rate of irritation and occasional allergy in highly reactive individuals, so I score it as moderate and advise patch testing for sensitive skin. Safety Notes: In real-world OTC skincare, caffeic acid is most often used as a minor antioxidant/soothing adjunct in complex botanical or polyphenol blends, where it can appear at trace-to-low levels around ~0.001–0.05% in leave-on serums/creams and some rinse-off cleansers. Higher-strength consumer products (typically leave-on antioxidant/brightening serums or water-free/oil-based systems using polyphenol complexes) are observed up to about 1–2%, beyond which stability (oxidation/darkening), solubility, and irritation/sensitization risk commonly limit practical formulation. No specific FDA/EU maximum is set for caffeic acid in cosmetics, so the upper end is driven primarily by formulatability and tolerability rather than regulation.

Caffeine

Caffeine is primarily used as a vasoconstrictive/anti-puffiness antioxidant, typically at ~0.1–3% in eye products and serums, and it is generally well-tolerated on intact skin. Clinical experience and patch-test data suggest low inherent irritancy, but stinging or dryness can occur in eczema-prone or barrier-impaired patients—especially in the periocular area or when paired with other actives—so it is best classified as gentle rather than very gentle. Safety Notes: In commercial skincare, caffeine is commonly used at very low levels (~0.01–0.1%) as a secondary/label-support ingredient in general moisturizers, cleansers, and body products, while eye-area de-puffing serums/creams and “energizing” leave-on treatments more typically sit around ~0.3–1%. High-strength consumer-available leave-on eye serums and slimming/firming body gels have been marketed up to about 5% caffeine, which is near the practical upper end due to solubility, crystallization risk, and sensory irritation constraints; rinse-off formats rarely justify higher levels because contact time is short.

Calamine

Calamine (primarily zinc oxide with a small amount of ferric oxide) is used topically in lotions/suspensions (commonly ~5–15%) as a soothing, antipruritic skin protectant and is generally well-tolerated even in eczema-prone skin. Clinically, true irritant reactions are uncommon, but dryness, transient stinging on fissured/compromised skin, or mechanical irritation from a drying, particulate film can occur, and rare contact allergy has been reported. Given its overall safety profile but non-zero risk in compromised barriers, it best fits a 'gentle' irritancy score. Safety Notes: In consumer skincare, calamine is used at very low levels (around 0.05–0.5%) as a soothing/anti-redness adjunct in lotions, creams, and masks where it functions mainly as a mild absorbent/opacifier. Mainstream OTC calamine anti-itch lotions are commonly formulated around 8% calamine, and the highest consumer-available leave-on suspensions/lotions and pastes are typically ~10–15% (often paired with zinc oxide), as higher loads become excessively chalky, unstable, and difficult to spread. Rinse-off products generally sit at the lower end since calamine’s benefit is primarily from leave-on contact time.