Alcohol Denat: Denatured ethanol: a fast-evaporating solvent that thins a formula and leaves a dry finish. International Chemical Safety Card ICSC 0044, Ethanol (anhydrous), prepared by an international group of experts for the ILO and WHO: "The substance defats the skin, which may cause dryness or cracking." WHO Guidelines on Hand Hygiene in Health Care (2009) records depletion of the skin lipid barrier by lipid-dissolving alcohols, and also that "the lipid-dissolving effect of alcohols is inversely related to their concentration". Both describe stronger exposures than a cosmetic formula.
Hamamelis Virginiana Extract: A tannin-rich astringent; the distillate sold under this name usually carries added alcohol, which is where the dry finish comes from. United States Pharmacopeia monograph "Witch Hazel", USP-NF version 02_01, DOI 10.31003/USPNF_M89070_02_01. The public DOI landing page carries a 2018 copyright and shows the definition, "Witch Hazel is a clear, colorless distillate prepared from recently cut and partially dried dormant twigs of Hamamelis virginiana L."; the specification, a distillate to which "150 mL of alcohol" is added per 850 mL at 14,0% to 15,0% ethanol, sits behind the USP subscription paywall. The monograph governs the pharmacopoeial article, not every product that prints this INCI name.
common irritantPropylene Glycol
Propylene Glycol: A solvent that shows up in patch-test clinics, more often as irritation than as allergy. American Contact Dermatitis Society, Allergen of the Year 2018 (Jacob SE, Scheman A, McGowan MA, Dermatitis 2018;29(1):3-5).
exfoliating acidLactic Acid
An alpha hydroxy acid that loosens surface skin cells; it also makes skin more sun-sensitive while you use it.
FDA, "Guidance for Industry: Labeling for Topically Applied Cosmetic Products Containing Alpha Hydroxy Acids as Ingredients" (announced at 70 FR 1721, 10 January 2005; FDA web pages title it "Labeling for Cosmetics Containing Alpha Hydroxy Acids"), which names this acid and recommends the statement "Sunburn Alert: This product contains an alpha hydroxy acid (AHA) that may increase your skin's sensitivity to the sun and particularly the possibility of sunburn."
humectantSodium PCA, Urea
Sodium PCA: The salt of PCA, one of the water-holding substances the outer layer of skin makes for itself. Dörner C, Steinbinder J, Sachslehner AP, Sukseree S, Eckhart L, "Amino Acid Metabolism of the Skin: Control by Specific Enzymes and Contribution to Protective Functions", Metabolites 2025;15(9):601, DOI 10.3390/metabo15090601, open access, section "Glutamine Is Converted to Pyrrolidone Carboxylic Acid, a Component of the NMF": "pyrrolidone carboxylic acid (PCA), also known as pyroglutamic acid or 5-oxoproline, accumulates in the stratum corneum."
Urea: A humectant the skin already makes; at higher levels it also softens thickened skin. StatPearls, "Moisturizers", NCBI Bookshelf NBK545171, updated 12 February 2024: "Urea is a component of NMF. The addition of urea to moisturizers helps with the absorption of water into the stratum corneum." The FDA label for prescription-strength urea calls it keratolytic and states that its mechanism of action is not yet known.
soothingNiacinamide
Niacinamide: A vitamin B3 form that supports the skin barrier and has anti-inflammatory activity; it turns up in products aimed at acne, rosacea and eczema. Camillo L, Zavattaro E, Savoia P, "Nicotinamide: A Multifaceted Molecule in Skin Health and Beyond", Medicina (Kaunas) 2025;61(2):254, DOI 10.3390/medicina61020254, PMID 40005371, open access: it "is extensively used in ... the treatment of dermatological conditions such as blistering diseases, atopic dermatitis, rosacea, and acne vulgaris", and contributes to reducing inflammation. On the acne evidence specifically: Liu H, Yu H, Xia J, Liu L, Liu GJ, Sang H, Peinemann F, "Topical azelaic acid, salicylic acid, nicotinamide, sulphur, zinc and fruit acid (alpha-hydroxy acid) for acne", Cochrane Database Syst Rev 2020;5:CD011368, DOI 10.1002/14651858.CD011368.pub2, PMID 32356369, records "low-quality evidence" for every nicotinamide comparison it could pool, and none of its four nicotinamide studies measured the physician global assessment at all.
