AHA Swipes

These describe what an ingredient is, not whether it is a problem. The stance marks above are the ratings; these are not.

• common irritantPropylene Glycol, Methylchloroisothiazolinone, Methylisothiazolinone

  • 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).
  • Methylchloroisothiazolinone: A preservative restricted to rinse-off products in the EU because of contact-allergy reports. EU Regulation (EC) 1223/2009, Annex V entry 39 (rinse-off only, 0,0015% of a 3:1 mixture with methylisothiazolinone). The reason is in Commission Regulation (EU) No 1003/2014, recital 3, quoted rather than summarised: "The SCCS concluded that the mixture of Methylchloroisothiazolinone (and) Methylisothiazolinone in a ratio of 3:1 does not pose a risk to the health of the consumer when used as a preservative up to a maximum authorised concentration of 0,0015 % in rinse-off cosmetic products, apart from its skin sensitising potential. The SCCS indicated that induction and elicitation would be less likely in a rinse-off product than when the same concentration is present in a leave-on product." SCCS/1238/09 concludes it "is well recognised as an important skin sensitiser at current conditions of use".
  • Methylisothiazolinone: A preservative that patch-test clinics see reactions to often enough that the EU banned it from leave-on products. American Contact Dermatitis Society, Allergen of the Year 2013 (Castanedo-Tardana MP, Zug KA, Dermatitis 2013;24(1):2-6); SCCS Opinion on Methylisothiazolinone (P94), Submission II, SENSITISATION ONLY (SCCS/1521/13, revision of 27 March 2014); banned in leave-on cosmetics by Commission Regulation (EU) 2016/1198, which recites the need to address "the increased incidence of allergies induced by methylisothiazolinone".

• exfoliating acidGlycolic Acid

  • Glycolic 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."

• humectantGlycerin, Sodium Hyaluronate

  • Glycerin: A humectant, and one of the two ingredients a comparison of moisturiser components found made a significant difference to skin hydration. FDA OTC skin protectant monograph, 21 CFR 347.10(h), lists glycerin as a skin protectant at 20 to 45%. On the humectant half: Jeong CB, Han JY, Cho JC, Suh KD, Nam GW, "Analysis of electrical property changes of skin by oil-in-water emulsion components", Int J Cosmet Sci 2013;35(4):402-410, DOI 10.1111/ics.12059, PMID 23621673, found that "glycerine and urea showed significant skin hydration effects compared with other humectants".
  • Sodium Hyaluronate: A humectant that holds a large amount of water at the skin surface. Chylińska N, Maciejczyk M, "Hyaluronic Acid and Skin: Its Role in Aging and Wound-Healing Processes", Gels 2025;11(4):281, DOI 10.3390/gels11040281, PMID 40277717, open access: hyaluronic acid's "high osmotic activity and anionic structure enable it to bind large amounts of water", and "sodium and potassium hyaluronate are widely used in moisturizing products". The same review notes that high-molecular-weight hyaluronic acid does not penetrate the deeper layers.