Do skincare acids make your skin sensitive to the sun?

Alpha hydroxy acids do. Research reviewed by FDA found that glycolic acid increased the skin's sensitivity to ultraviolet light. FDA recommends a sunburn alert on leave-on AHA cosmetics: use sunscreen, wear protective clothing and limit sun exposure while using the product and for a week afterwards. The same habit makes sense with salicylic acid.

Which acids this covers

Exfoliating acids in skincare fall into three groups.

• Alpha hydroxy acids (AHAs): glycolic acid, lactic acid, mandelic acid, citric acid, malic acid and tartaric acid. FDA's sun-sensitivity guidance addresses this group.
• Beta hydroxy acid (BHA): salicylic acid, which is oil-soluble and works in pores as well as on the surface.
• Polyhydroxy acids (PHAs): gluconolactone and lactobionic acid, larger molecules used for a gentler exfoliation.

All of them loosen the bonds between dead cells on the skin surface. One explanation offered in the literature for the added sun sensitivity is that a thinner layer of dead cells leaves skin less shielded from ultraviolet light.

What the research found

In a study published in 2003, Kaidbey and colleagues applied glycolic acid to volunteers' skin for several weeks, then exposed treated and untreated sites to ultraviolet light. The treated skin was more sensitive: it reddened more readily and formed more sunburn cells. A week after application stopped, the difference had gone.

The US Cosmetic Ingredient Review had reached a related conclusion in 1998: glycolic and lactic acid are safe in consumer products when the product is formulated to avoid increasing sun sensitivity, or when its directions call for daily sun protection.

What FDA recommends

FDA's 2005 guidance for industry recommends this statement on cosmetics containing alpha hydroxy acids:

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. Use a sunscreen, wear protective clothing, and limit sun exposure while using this product and for a week afterwards.

The guidance is written for AHAs. The evidence on salicylic acid is less clear. Daily sun protection is the sensible habit with any exfoliating acid.

How to use acids with the sun in mind

• Use acids in the evening. Apply sunscreen every morning, whatever the weather and whether or not you used an acid the night before.
• Choose a broad-spectrum sunscreen and apply enough of it. Reapply as its label directs when you are outdoors. How sunscreen filters work: UV filters.
• Cover up and seek shade in strong sun. Sunscreen is one layer of protection, not the only one.
• Keep going for a week after you stop. The added sensitivity fades over about a week.
• Pause before sun-heavy plans. Before a beach holiday or a ski trip, many people stop acids a week ahead.
• Start slowly. A few evenings a week, then build up. Do not stack several exfoliating products in one routine.
• Stop if skin stings, peels or stays red. Early bumps are often called "purging"; what that term covers: the purging myth.

Who should take extra care

• Skin that burns easily or reacts readily.
• Anyone also using a retinoid, which adds its own sensitivity.
• Anyone who has just had a professional procedure. Acids wait until the practitioner clears them. See can you apply a serum after microneedling? and chemical peels.
• Anyone taking a medicine that increases sun sensitivity. Ask your pharmacist or physician.

Vegalab products that contain acids

Brightening NanoSerum, sealed vial set, contains glycolic acid, mandelic acid and lactic acid. The FDA sunburn alert above applies to it. Format: Brightening NanoSerum, Sealed Vial Set.

Clarifying NanoSerum, sealed vial set, contains salicylic acid. Use daily sun protection with it. Format: Clarifying NanoSerum, Sealed Vial Set.

To find acids in any product, check its ingredient list for the names above: how to read an ingredient list.

Clinic questions on acids, sequencing and aftercare: professional FAQ. More guides: Beauty Science knowledge.

Sources

• US Food and Drug Administration. Guidance for Industry: Labeling for Topically Applied Cosmetic Products Containing Alpha Hydroxy Acids as Ingredients. January 2005.
• Kaidbey K, Sutherland B, Bennett P, et al. Topical glycolic acid enhances photodamage by ultraviolet light. Photodermatol Photoimmunol Photomed. 2003;19(1):21-27.
• Cosmetic Ingredient Review. Final report on the safety assessment of glycolic acid, ammonium, calcium, potassium, and sodium glycolates, methyl, ethyl, propyl, and butyl glycolates, and lactic acid, ammonium, calcium, potassium, sodium, and TEA-lactates, methyl, ethyl, isopropyl, and butyl lactates, and lauryl, myristyl, and cetyl lactates. Int J Toxicol. 1998;17(Suppl 1):1-241.
• Kornhauser A, Coelho SG, Hearing VJ. Applications of hydroxy acids: classification, mechanisms, and photoactivity. Clin Cosmet Investig Dermatol. 2010;3:135-142.