Skincare Ingredients

Thioctic Acid

Thioctic acid (alpha-lipoic acid) is an antioxidant typically used around ~0.1–1% in topical products, and it has a documented propensity to cause stinging, erythema, or irritant reactions in reactive skin—especially when formulated at lower pH or in alcohol-heavy vehicles. While many users tolerate it, eczema-prone and barrier-impaired patients show a higher risk of irritation and occasional sensitization signals in patch testing/usage reports, so I score it as moderate with patch testing strongly recommended. Safety Notes: Thioctic acid (alpha-lipoic acid) appears in consumer skincare primarily as a leave-on antioxidant/anti-aging active, with low-end usage around 0.01–0.1% in multi-antioxidant serums and moisturizers where it is a supporting ingredient. Dedicated ALA serums/creams commonly sit around ~0.5–1%, while the highest-strength OTC specialty products marketed for intensive antioxidant/texture benefits reach about 3–5% (above this, stability/odor/irritation and formulation challenges become limiting in consumer cosmetics). It is uncommon in rinse-off products, and the observed market maximum is mainly in leave-on serums/creams with solubilization and stabilization aids.

Thiotaurine

Thiotaurine is an antioxidant/osmoprotective sulfur-containing amino-acid derivative typically used at low concentrations (about 0.1–1%) to help mitigate oxidative stress, and it is not a pH-dependent exfoliating active. Available safety use data and its close structural similarity to well-tolerated endogenous osmolytes suggest a low inherent irritancy profile, with only occasional stinging possible on severely compromised barriers. Given the limited breadth of large-scale patch-test data in highly reactive eczema populations, I score it as very gentle rather than exceptionally gentle for patient safety. Safety Notes: In commercial skincare, thiotaurine is most often used as an anti-pollution/antioxidant active at low tenths of a percent; I have observed it at ~0.01% in multi-ingredient antioxidant/soothing serums where it functions as a minor supportive active. Higher-strength consumer leave-on products (serums/ampoules/eye gels marketed for anti-stress/anti-pollution or blue-light defense) have been marketed around 1–2%, with ~2% representing the upper end typically seen before solubility, cost, and overall formula osmolality/skin feel become limiting; rinse-off use is less common and generally trends toward the lower end.

Threonine

MVP Approved - Threonine is an amino acid used in skincare formulations for its moisturizing (hydrating) and anti-aging properties, and it is generally well-tolerated with a very low risk of irritation.

Thymol

Thymol is a phenolic terpene (thyme-derived) used for antimicrobial/deodorizing effects, typically at low but biologically active concentrations, and it is a well-recognized skin and mucosal irritant in patch testing and real-world use. As a lipophilic phenol it can disrupt the stratum corneum and provoke stinging/burning, with higher risk in eczema or barrier-impaired skin and when layered with other actives. Given its consistent irritancy potential and the frequency of reactions in sensitive populations, it warrants a significant score. Safety Notes: In mainstream OTC skincare, thymol is most often used as a minor antimicrobial/deodorizing constituent within essential-oil/fragrance systems or preservative-boosting blends, with commercial leave-on and rinse-off products commonly sitting around ~0.001–0.05% due to odor and irritation constraints. The highest consumer-available levels observed are in niche antiseptic/deodorant or anti-blemish formulas and some foot/scalp products where thymol is used as a primary antimicrobial active, reaching about 0.1–0.5% in OTC leave-on or short-contact products. Above ~0.5% is uncommon in mass-market cosmetics because thymol becomes strongly scented and can increase sensitization/irritation risk, so such strengths tend to be reserved for drug/professional products rather than general consumer skincare.

Thymus Vulgaris Extract

Thymus vulgaris (thyme) extract is a botanical antimicrobial/antioxidant that can contain sensitizing fragrance components (e.g., thymol/carvacrol) depending on extraction method, and it has documented potential to trigger irritation or allergic contact dermatitis in reactive or eczematous skin. In typical leave-on cosmetic use levels, many tolerate it, but the variability in composition and higher risk in compromised barriers warrants treating it as a notable irritant that should be introduced cautiously and patch tested. Safety Notes: In mass-market leave-on skincare (serums, moisturizers, toners) Thymus vulgaris extract is often used as a supporting antioxidant/clarifying botanical at very low levels (commonly as part of a botanical blend), with observed use down to ~0.0005% when supplied as a concentrated extract or within multi-extract complexes. Higher-strength consumer products positioned for oily/acne-prone skin, deodorizing, or scalp/clarifying benefits (including some masks and shampoo/cleanser systems) can reach ~1–2% as the neat extract, with rinse-off formulas typically tolerating the upper end due to reduced skin contact time and odor/sensitization constraints from thyme constituents.

Thymus Vulgaris Oil

Thymus Vulgaris (thyme) oil is a highly concentrated essential oil rich in thymol and carvacrol, compounds with well-documented irritant and sensitization potential, even at low leave-on concentrations (often well below 1%). Clinical patch testing and case reports show essential oils are common triggers for allergic contact dermatitis and can markedly flare eczema due to barrier disruption. Given the high risk in sensitive and compromised skin and the potential for delayed sensitization, it warrants a very high irritancy score. Safety Notes: In mass-market leave-on skincare (creams/lotions/serums), Thymus vulgaris (thyme) oil is typically used at very low fragrance/antimicrobial-support levels (often ~0.0005–0.05%) due to sensitization/irritation potential and IFRA-restricted allergen components (e.g., thymol, carvacrol, linalool). Higher consumer-available concentrations are seen in rinse-off cleansing products and some niche “clarifying”/essential-oil-forward spot or scalp treatments, where total thyme oil can reach ~0.2–1.0% while remaining OTC; above ~1% is uncommon in mainstream skincare because odor intensity, dermal tolerance, and IFRA compliance become limiting.

Tilia Cordata Extract

Tilia cordata (linden) flower/leaf extracts are typically used at low concentrations as soothing/antioxidant botanicals, but botanical extracts remain a common source of stinging, erythema, and occasional allergic contact dermatitis in sensitized or eczematous patients due to complex mixtures of plant proteins and polyphenols. While many users tolerate it, clinical patch testing experience with botanicals supports a non-trivial risk of reactivity in highly sensitive skin, so I rate it as mild rather than “gentle” for compromised barriers. Safety Notes: In mass-market and premium moisturizers/toners/cleansers, Tilia cordata (linden) extract is commonly used as a low-level soothing/marketing botanical, with real-world INCI placements consistent with ~0.001–0.1% (especially in rinse-off where botanicals are often token-dosed). Higher-strength consumer products (botanical serums, calming masks, and “herbal” gels/creams) use supplier-recommended active-use levels around 0.5–3%, and some niche formulas push to ~5% when the extract is the featured active and stability/odor/color are managed. No specific EU/FDA maximum applies to this botanical extract, so practical limits are driven by sensorial impact, cost, and preservative system compatibility rather than regulation.

Tin Oxide

Tin oxide is an inert inorganic pigment/opacifier used at low levels in color cosmetics (commonly a few percent) to add opacity and shimmer. It is generally non-reactive and not a common irritant or sensitizer in patch-testing, but as a particulate mineral it can cause occasional mechanical irritation in highly reactive or compromised skin (especially around the eyes), so it is best rated very gentle rather than fully inert. Safety Notes: Tin Oxide is most commonly used as a pearlescent/opacity modifier in color cosmetics and some skincare-makeup hybrids; at the low end it appears as a trace component (~0.01–0.1%) when supplied as part of mica/TiO2/SnO2 effect pigment blends in leave-on products. Higher levels occur in shimmer/highlighter products and radiant primers where SnO2 is used as a discrete effect pigment component, with total SnO2 commonly in the low single-digits and reaching the low-teens (~10–15%) in highly pearlescent consumer formulations. It is uncommon in rinse-off skincare and, where present, is typically at the low end due to limited benefit and cost/handling considerations.

Titanium Dioxide

Titanium dioxide is an inert mineral pigment/UV filter typically used at a few percent up to ~25% in sunscreens and is considered non-sensitizing and non-irritating in standard patch testing, including for sensitive skin. In real-world use, irritation is uncommon and usually relates to formulation factors (vehicle, rubbing, or inhalation risk with loose powders) rather than the ingredient itself. Given compromised-skin populations, I rate it as exceptionally gentle rather than perfectly inert. Safety Notes: In commercial skincare, titanium dioxide is seen at very low levels (~0.05–1%) as an opacifier/whitener in lotions, cleansers, and moisturizers (including rinse-off), where it’s not intended to provide UV protection. At the high end, consumer mineral sunscreens and tinted SPF products commonly use ~5–20% titanium dioxide, with some high-coverage stick/cream and high-SPF mineral formulations reaching about 25% to achieve SPF/UVA performance and opacity; these are leave-on products. Regulatory frameworks generally do not set a uniform max % across all markets, but TiO2 is widely permitted in cosmetics/sunscreens with usage constrained in practice by aesthetics, dispersion, and photostability/coverage requirements.

Tocopherol

MVP Approved - Tocopherol (Vitamin E) is a lipid‐soluble antioxidant commonly used in skincare for its anti-aging, moisturizing, and skin-healing properties, and it is generally well-tolerated with low irritancy at typical usage levels.

Tocopheryl Acetate

Tocopheryl acetate (vitamin E acetate) is primarily an antioxidant/emollient used typically around ~0.1–5% in leave-on products and is generally well tolerated in clinical use. However, patch testing and case reports document occasional allergic contact dermatitis to vitamin E derivatives, and the risk increases in eczema-prone or highly reactive skin and with repeated exposure in multi-step routines. Given its overall low irritancy but real sensitization potential in a vulnerable subset, it fits best as a gentle ingredient rather than exceptionally gentle. Safety Notes: In mass-market lotions, facial moisturizers, sunscreens, and many rinse-off cleansers, tocopheryl acetate is often used as a label/antioxidant-support ingredient at very low levels (~0.01–0.1%), with more typical leave-on usage commonly around 0.2–1%. High-strength consumer-available formulations (e.g., vitamin E oils/serums, anhydrous balms, and targeted antioxidant treatments) can reach several percent, with upper-end OTC products observed up to ~10% while still remaining cosmetically stable and sensorially acceptable. There is no specific FDA/EU maximum for tocopheryl acetate in cosmetics, so practical stability/feel and irritation risk tend to set the market ceiling rather than regulation.

Tocopheryl Linoleate

Tocopheryl linoleate is an esterified form of vitamin E used as an emollient/antioxidant in leave-on products typically at low concentrations, and it is generally well tolerated. However, vitamin E derivatives can occasionally trigger irritant or allergic contact dermatitis in eczema-prone or highly reactive individuals, and the linoleate (unsaturated lipid) can oxidize over time, increasing sensitization risk in compromised skin. Overall, the baseline irritation potential is low but not negligible, supporting a gentle (not exceptionally gentle) score. Safety Notes: In commercial skincare, tocopheryl linoleate is most often used as an antioxidant/emollient vitamin E derivative at very low levels (typically ~0.01–0.1%) in leave-on creams/lotions and even lower-end inclusions in rinse-off cleansers where contact time is short. Higher-strength consumer products (facial oils, lipid serums, barrier creams) use it as part of the oil phase or an “active” vitamin E complex, with observed OTC market levels reaching ~2–5% in leave-on formats; above this is uncommon due to cost, oxidative stability/odor considerations, and diminishing formulation benefit. No specific EU/FDA concentration cap is typically applied to tocopheryl linoleate in cosmetics, so the practical upper limit is driven mainly by stability and sensorial constraints.

Tocopheryl Nicotinate

Tocopheryl nicotinate is a vitamin E–nicotinate ester used in leave-on products for “microcirculation/brightening” effects, typically at low percentages, but it can cause noticeable vasodilation with warmth, flushing, and stinging in reactive skin. Clinically, nicotinate derivatives are well known to provoke erythema and discomfort, and in eczema-prone or barrier-impaired users this can translate into significant irritation even at typical cosmetic concentrations. Given its predictable flush/sting potential and the need for careful introduction, it warrants a significant irritancy score. Safety Notes: In commercial skincare, tocopheryl nicotinate is most often used as a low-level circulation/skin-conditioning adjunct in leave-on creams/lotions and eye/face products, commonly appearing around 0.01–0.3% when included as part of a broader antioxidant/vitamin complex. Higher-strength OTC “warming”/microcirculation or firming creams and specialty treatment creams have been marketed with tocopheryl nicotinate in the ~1–5% range, with 5% representing the upper end observed for consumer-available leave-on products due to increased risk of flushing/irritation at higher levels; it is uncommon in rinse-off formats and typically used at lower levels there when present.

Tocopheryl Succinate

Tocopheryl succinate is a vitamin E ester used as an antioxidant/skin-conditioning agent, typically at low concentrations (~0.1–2%), and is generally well tolerated. However, vitamin E derivatives have documented, albeit uncommon, irritation and allergic contact dermatitis in patch testing and in eczema-prone patients, especially in leave-on products and when formulations are otherwise sensitizing. Given this low-but-real risk in highly reactive skin, it fits a 'gentle' rather than 'very gentle' score. Safety Notes: In mass-market leave-on moisturizers, sunscreens, and cleansers, tocopheryl succinate is often used as a secondary antioxidant/skin-conditioning agent at very low levels (~0.01–0.2%), frequently alongside other tocopherol forms. Higher-strength consumer serums, ampoules, and antioxidant creams have been marketed with tocopheryl succinate in the ~1–5% range to position a “vitamin E derivative” claim; above ~5% is uncommon in OTC products due to cost, oil-phase/solubility constraints, and sensorial/stability considerations. There is no specific EU/FDA maximum for this ingredient in cosmetics, so observed limits are primarily driven by formulation practicality rather than regulation (leave-on and rinse-off both occur, with the highest levels typically in leave-on products).

Tocotrienols

MVP Approved - Tocotrienols, a form of vitamin E, are used in skincare for their potent antioxidant and anti-aging properties while generally being well-tolerated.

Totarol

Totarol is a diterpene phenolic antimicrobial/antioxidant (often sourced from totara tree) used in leave-on and oral-care products typically around ~0.05–0.5% for preservative/anti-acne support. Phenolic antimicrobial botanicals have a meaningful history of causing irritant reactions and occasional allergic contact dermatitis in patch-testing/clinical use, especially on compromised barriers (eczema, retinoid/AHA users) and when combined with other actives. Given its bioactive, antimicrobial nature and sensitization potential in a sensitive-skin population, I rate it as a moderate irritant where patch testing and cautious introduction are warranted. Safety Notes: In commercial OTC skincare and oral-care adjacent cosmetics (e.g., anti-blemish gels, toners, deodorant-style skin products), totarol is commonly used at very low levels (~0.01–0.05%) as an antimicrobial/anti-inflammatory booster, often in leave-on formats. Higher-strength consumer products marketed for acne/blemish control and oily skin have been observed around 0.2–0.5%, with the upper end near ~1.0% in specialized leave-on spot treatments/serums where odor, solubility, and irritation potential become practical constraints. Totarol is typically not used at meaningful levels in rinse-off cleansers due to brief contact time, so the market maximum is primarily driven by leave-on products.

Tranexamic Acid

Tranexamic acid is a pigment-modulating active typically used topically around 2–5% in leave-on products, and while it is generally well-tolerated, clinical use and consumer data do document occasional stinging, dryness, or erythema—especially when layered with other actives. It is not an exfoliating acid and is far less predictably irritating than AHAs/BHAs or retinoids, but in reactive/eczema-prone skin the risk is still meaningful enough to classify as mild rather than gentle. Safety Notes: In consumer skincare, tranexamic acid is most commonly found in leave-on brightening serums/creams, with low-end inclusion around 0.1–0.3% in multi-active tone-correcting formulas (and some rinse-off products). Mainstream OTC products typically sit around 2–5%, while a small number of high-strength, consumer-available specialty serums reach ~8–10%; above this is uncommon due to solubility/pH, sensory, and irritation/stinging constraints rather than an explicit cosmetic regulatory cap.

Trehalose

MVP Approved - Trehalose is a natural sugar used as a humectant in skincare, prized for its ability to hydrate the skin while causing minimal irritation.

Tremella Fuciformis Sporocarp Extract

Tremella fuciformis (snow mushroom) sporocarp extract is primarily a humectant/film-forming polysaccharide used at low percentages in moisturizers and serums, and it is generally well-tolerated with a low rate of irritation in cosmetic use. While not an exfoliating active, botanical extracts can rarely trigger irritation or allergy in highly reactive or eczema-prone patients (including due to trace impurities or preservation systems), so it is not scored as inert. Overall, it fits "very gentle" for most sensitive skin when properly formulated. Safety Notes: In mass-market and prestige leave-on products (creams/lotions/toners/cleansers), Tremella fuciformis (snow mushroom) sporocarp extract is often used as a low-level label claim or supporting humectant at ~0.001–0.1%, especially when supplied in diluted glycerin/butanediol carriers. Dedicated hydrating serums/masks frequently place it in the 0.2–2% range, while a small number of consumer-available “high-strength” formulas using concentrated extract powders or high active-load blends reach ~3–5% in leave-on products before viscosity, tack, and stability constraints become limiting; rinse-off products generally sit at the low end due to reduced deposition time. No specific FDA/EU maximum applies, so the observed upper end is driven mainly by sensorial and formulation stability considerations rather than regulatory caps.

Triacetin

Triacetin (glycerol triacetate) is primarily a solvent/plasticizer and viscosity-modifying ingredient used at low percentages in cosmetics, and it is generally well tolerated with low rates of irritation in standard use. While not completely inert, it is not a sensitizing fragrance component and is less likely to sting compromised skin than many common solvents (e.g., alcohols or propylene glycol). For severe eczema or highly reactive patients, rare irritant reactions can still occur, but overall clinical risk supports a very gentle score. Safety Notes: Triacetin (glycerol triacetate) is used in consumer skincare primarily as a solvent/plasticizer for fragrance and as a humectant/skin-conditioning adjunct, where it is often present at very low levels (~0.05–1%) in lotions, cleansers, and makeup to aid solubilization and sensory. Higher levels are observed in anhydrous or low-water leave-on formats (e.g., perfume/fragrance-adjacent skin oils, certain deodorants/antiperspirants, and specialty solvent-base serums/primer-type products) where it can function as a major carrier and reach ~10–30% in OTC products. There is no specific EU/FDA cosmetic maximum for triacetin; practical limits are driven by odor/feel, solvency needs, and compatibility with the rest of the formula (rinse-off typically stays at the low end, while leave-on solvent systems account for the high end).

Tribehenin

Tribehenin is a non-volatile waxy lipid (triglyceride of behenic acid) used mainly as an emollient/thickener in creams, balms, and lip products, typically at low-to-moderate percentages, and it is not an active with pH-dependent irritation. As a large, inert fatty material it has very low irritancy and is generally well-tolerated in patch testing and in eczema-prone skin, with reactions being uncommon and more often related to overall formula factors rather than the ingredient itself. Given the need to be cautious for highly compromised skin while acknowledging its excellent tolerability, it fits “exceptionally gentle” rather than truly inert. Safety Notes: In commercial skincare, tribehenin is most often used as a minor viscosity builder/structurant and emollient in leave-on creams/lotions and cleansing balms, commonly appearing around ~0.1–2% when used mainly for texture and payoff. At the high end, it is found in consumer-available anhydrous balm/stick formats (e.g., cleansing balms, ointment-style barrier balms, solid moisturizers) where it functions as a primary lipid structurant and can reach roughly 10–25% depending on the oil/wax system. No specific EU/FDA concentration cap is established for tribehenin in cosmetics; practical limits are driven by melt profile, hardness, and sensory/stability constraints rather than regulatory thresholds.

Tribehenin PEG-20 Esters

Tribehenin PEG-20 esters are non-ionic PEG-modified lipid esters used mainly as emulsifiers/solubilizers at low concentrations (commonly ~0.5–5%), and they are generally well-tolerated in routine patch testing with low rates of irritant reactions. In highly reactive or eczema-prone skin, PEG-modified surfactant-like materials can very occasionally sting or contribute to barrier disruption when layered with other actives, but the ingredient itself is typically very gentle and not a primary irritant. Safety Notes: In commercial leave-on skincare (creams, lotions, sunscreens, makeup-skincare hybrids), Tribehenin PEG-20 Esters is most often used as a solubilizer/co-emulsifier or texture modifier at low levels around 0.1–1%. Higher-strength consumer products such as anhydrous cleansing balms, heavy ointment-like moisturizers, and rich balm-to-milk makeup removers can use it as a primary structuring/emulsifying component in the ~5–15% range. Rinse-off formats typically sit toward the low-to-mid end unless formulated as balm cleansers that emulsify on contact with water.

Tricaprylin

Tricaprylin is a medium-chain triglyceride emollient/solvent used at relatively high levels in skincare to improve slip and reduce transepidermal water loss; it is generally well-tolerated and commonly used in sensitive-skin formulas. Clinical and patch-test experience shows a low rate of irritation/sensitization compared with surfactants, acids, or fragrances, though rare irritant or follicular intolerance can occur in highly reactive patients or with occlusive layering. Given its broad compatibility but non-zero risk in compromised barriers, it best fits a very gentle score rather than completely inert. Safety Notes: In commercial skincare, tricaprylin is frequently used at low levels (~0.1–2%) as a slip/emollient and solvent for oil-soluble actives in leave-on serums, lotions, sunscreens, and makeup; rinse-off products also use it in this low single-digit range as part of the emollient phase. At the high end, it appears as a primary/major carrier oil in anhydrous facial oils, cleansing oils/balms, and oil-based active concentrates, reaching ~50–90% and, in some consumer-available single-ingredient oil products, up to 100%. There is no specific EU/FDA maximum concentration restriction for tricaprylin itself in cosmetics, so practical use is governed mainly by sensorial goals, solubilization needs, and product format.

Tridecane

Tridecane is an inert, nonpolar hydrocarbon used primarily as an emollient/solvent in low-to-moderate amounts; it is not an active and does not have inherent pH-dependent or reactive chemistry that typically drives irritation. Available safety and patch-test experience for similar cosmetic alkanes indicates a low rate of irritation/sensitization, with reactions mainly attributable to individual intolerance or impaired barrier states rather than the ingredient itself. For severe eczema or post-procedure skin I still avoid calling it “inert,” so it scores as very gentle rather than 0.0. Safety Notes: Tridecane is most commonly encountered in consumer skincare as part of lightweight emollient/solvent systems (often paired with undecane) where it can appear at low levels (~0.1–1%) in leave-on creams/serums for slip and sensory improvement. In many commercial INCI decks it is used as a primary hydrocarbon emollient/vehicle phase, with mid-range use around 2–10% and high-strength “dry oil”/waterless serum, primer, and makeup-adjacent skincare formats reaching ~15–20% while remaining OTC. There are no specific EU/FDA cosmetic concentration limits for tridecane itself; practical upper use levels are driven by sensorial targets, volatility/flash point considerations, and compatibility with packaging and other oils.

Trideceth-12

Trideceth-12 is a nonionic surfactant/solubilizer used at low-to-moderate levels in cleansers and leave-on products, but surfactants can disrupt the stratum corneum and increase stinging, especially on eczema-prone or compromised skin. Patch-test and in-use data generally show low irritation potential at typical concentrations, yet reactive individuals can experience barrier-related irritation (more so in combination with other surfactants, acids, or fragrances). For patient safety in highly sensitive populations, I rate it as mild rather than “gentle.” Safety Notes: In commercial leave-on skincare (serums, creams, sunscreens) Trideceth-12 is typically used as a nonionic solubilizer/emulsifier or co-surfactant at very low levels (~0.05–1%) to aid fragrance/oil solubilization and improve emulsion stability/feel. Higher concentrations are observed in consumer-available high-surfactant systems (cleansing oils, micellar/waterless cleansing concentrates, makeup removers, and some hair/scalp cleansing products) where it can function as a primary or major co-surfactant, reaching ~3–10% in strong rinse-off or remover formulas; above this is uncommon in OTC skincare due to irritation/feel and formulation balance constraints.

Trideceth-6

Trideceth-6 is a nonionic ethoxylated surfactant/solubilizer used at low levels (often ~0.1–5%) to help disperse oils and fragrances, but surfactant-type ingredients can disrupt the stratum corneum and provoke stinging, especially on compromised or eczematous skin. In patch testing and real-world use, irritation is generally uncommon at typical leave-on concentrations yet clearly possible in reactive individuals, particularly when combined with other cleansing agents or fragrance systems. Given the higher risk in barrier-impaired patients and cumulative routine exposure, a mild irritancy score is the safest clinically-aligned assessment. Safety Notes: Trideceth-6 is a nonionic surfactant/solubilizer most often used at very low levels (~0.05–0.5%) in leave-on products (serums, sprays, toners) to solubilize fragrance/oils or aid emulsion stability, and around ~0.5–3% in cleansing systems to support mildness and foam/solubilization. In consumer-available high-surfactant formats (micellar waters, cleansing oils/balms converted to self-emulsifying cleansers, makeup removers, and some exfoliating cleansers), total ethoxylated surfactant packages can be high and Trideceth-6 is observed up to ~10–15% as part of the primary solubilizing/emulsifying system; rinse-off products dominate the upper end due to potential irritation/tack at high leave-on levels.

Tridecyl Salicylate

Tridecyl Salicylate is an ester of salicylic acid used mainly as an emollient/fragrance component and does not function as an exfoliating BHA at typical cosmetic use levels (generally low). As a high–molecular weight, lipophilic ester, it has low water solubility and limited bioavailability, so routine irritation potential is low; however, because it is a salicylate derivative and can be present in fragranced formulas, a small risk of irritation/sensitization exists in highly reactive or eczema-prone patients. Safety Notes: Tridecyl Salicylate is most commonly encountered as a fragrance/fixative component or emollient ester, where it appears at trace-to-low levels in leave-on skincare and haircare (often ~0.01–0.3%) and sometimes up to ~1% when used to support sensory slip. In consumer-available OTC products positioned as perfumed body lotions, oils, and some specialty fragrance-forward formulations, it can be used at several percent as part of the oil/fragrance phase, with upper market observations around ~3–5% (higher would typically be limited by odor profile, cost, and overall perfume load rather than a specific global regulatory cap). Leave-on products generally sit lower than rinse-off due to cumulative fragrance exposure considerations, but both formats can span the stated range.

Tridecyl Stearate

Tridecyl Stearate is a fatty ester emollient used to improve slip and reduce water loss, typically at low-to-moderate concentrations in creams and makeup. Fatty esters like this are generally considered non-sensitizing and show very low rates of irritation in patch testing, with reactions usually limited to rare, highly reactive individuals or in the setting of severely compromised barriers. Given its inert, occlusive/emollient profile and minimal clinical irritancy signal, it fits an exceptionally gentle score. Safety Notes: Tridecyl Stearate is used as an emollient/texture agent and slip modifier, and in many commercial leave-on products it appears at low levels (~0.05–1%) as part of a larger ester/emollient blend to tune sensorial feel. In richer leave-on creams, balms, and color cosmetics (e.g., long-wear lip products, moisturizers, and anhydrous sticks), it can be a primary emollient/wax-ester component, with observed consumer-market use commonly reaching 10–20% and occasionally up to ~25% in high-slip, high-occlusivity specialty formulations. It is uncommon in rinse-off at high levels due to wash-off and cost/feel considerations, so the upper end is primarily driven by leave-on and anhydrous systems.

Tridecyl Trimellitate

Tridecyl Trimellitate is a high–molecular weight emollient/film-forming ester commonly used in leave-on products (often a few percent up to higher levels in color cosmetics) to improve slip and reduce transepidermal water loss. As a non-volatile, non-reactive lipid-like material, it has low inherent irritancy in patch testing and lacks the pH-dependent or biologically active mechanisms that drive stinging/burning. In very reactive or eczema-prone patients, occlusion or individual intolerance is still possible, but clinically it aligns best with a very gentle, low-risk profile. Safety Notes: Tridecyl Trimellitate is used as an emollient/film former and pigment wetting/binder in leave-on color cosmetics and some skincare; in broader skincare it often appears at low supportive levels (~0.1–2%) to improve slip and reduce tack in creams/lotions and sunscreen vehicles. In long-wear lip products, foundations, and other high-payoff anhydrous or low-water systems marketed OTC, it can be a major part of the oil phase and is observed in the ~10–40% range, with the upper end driven by high-gloss/long-wear, transfer-resistant formats. It is uncommon in rinse-off products (typically low, if present) since its performance benefits are primarily for leave-on film formation and wear.

Triethanolamine

Triethanolamine is primarily a pH adjuster/emulsifier used at low concentrations (often ~0.5–3%) to neutralize fatty acids and stabilize formulas; at these levels it is generally well tolerated. However, clinical experience and patch testing data show it can cause irritant contact dermatitis—especially in compromised barriers (eczema, post-procedure) or when used to raise product pH—and it has occasional sensitization reports. Given the non-trivial irritation potential in reactive patients and its routine presence in leave-on products, a mild risk score is warranted for patient safety. Safety Notes: In commercial skincare, triethanolamine (TEA) is most often used at low levels (~0.05–0.5%) as a pH adjuster/neutralizer for carbomer or acrylic thickeners in leave-on lotions, serums, and sunscreens, and in rinse-off cleansers. Higher-strength consumer products (e.g., certain hair-removal/depilatory creams, strong soap-free cleansing creams, and some high-alkaline cream systems) can use TEA in the ~1–5% range to neutralize fatty acids or polymers and build structure; above this is uncommon in OTC cosmetics due to irritation potential and nitrosamine-control considerations under EU/FDA good manufacturing practice.