Should glycolic acid be avoided during exposure to sunlight?

Glycolic acid, sourced from sugar cane, is a small molecule that penetrates the skin readily. It acts by disrupting the bonds between dead skin cells, thereby promoting exfoliation and revealing smoother, brighter skin. While it is effective at improving texture and hyperpigmentation, glycolic acid may heighten the skin’s sensitivity to ultraviolet (UV) radiation.

Studies demonstrate that glycolic acid can indeed increase the skin’s photosensitivity. One seminal study by Kornhauser A. et al. (2003) applied 10% glycolic acid (pH 3.5) to the backs of 29 Caucasian volunteers. Following four weeks of daily application, the treated areas were exposed to UV radiation. The findings revealed that regions treated with glycolic acid exhibited heightened sensitivity to UV light, as evidenced by an elevated number of sunburn cells (SBCs) and a reduced minimal erythema dose (MED), defined as the lowest dose of UV radiation required to produce visible redness or erythema (sunburn) on the skin.

Interestingly, while cyclobutyl pyrimidine dimers (CPDs) in DNA—markers of UV-induced damage—were elevated, they did not reach statistical significance. This suggests that glycolic acid exacerbates superficial damage (such as erythema and SBCs) but may not appreciably affect deeper DNA lesions in this context.

The good news is that this photosensitising effect seems to be temporary. The same study observed that ceasing glycolic acid use for a week allowed the skin’s sensitivity levels to return to normal. This implies that with appropriate timing and protection, glycolic acid use does not have long-lasting photosensitising effects.

The exact mechanism by which glycolic acid increases photosensitivity is not fully understood. Unlike chemical sunscreens, glycolic acid does not absorb UV radiation directly. Research suggests that its photosensitising effect could stem from its ability to exfoliate and thin the stratum corneum, the skin’s outermost layer. By removing this protective layer, glycolic acid might make the skin more susceptible to UV penetration.

A report by ANDERSEN F. A. (1998) supports this, emphasising that the exfoliating action of glycolic acid can render the skin more susceptible to UV radiation damage. This effect aligns with the findings of HONG J. T. & al. (2002), who noted increased skin damage when glycolic acid was used in conjunction with UVB exposure. However, HONG’s study also found that this enhancement occurred without elevating inflammation markers such as PGE2 or COX-2, indicating a specific interaction at the epidermal level rather than deeper inflammatory processes.

Interestingly, the study also investigated salicylic acid, another commonly used exfoliant. Despite its exfoliating properties, salicylic acid did not exhibit the same photosensitising effects as glycolic acid. This suggests that the mechanism underlying glycolic acid’s photosensitising effect remains theoretical, and further research is needed to fully understand why glycolic acid increases sensitivity to sunlight.

In light of these findings, it is prudent to exercise caution when employing glycolic acid formulations should you anticipate exposure to sunlight. Below are some key recommendations:

• Cover the Treated Area: Where possible, cover the area where glycolic acid was applied. If it is the face, try to avoid direct sunlight and consider wearing a hat or employing other physical barriers for additional protection.

• Use suncream: Always apply a broad-spectrum suncream with a high SPF when using glycolic acid. Suncream can help mitigate the increased risk of sunburn and UV-induced damage.

• Timing Matters: To minimise risks, apply glycolic acid products in the evening. This reduces the likelihood of immediate sun exposure following application. For individuals frequently exposed to the sun, reducing glycolic acid usage or switching to less photosensitising alternatives during the summer months may be advisable.

• Monitor Your Skin: If you experience redness or irritation, it may be prudent to suspend the use of glycolic acid or reduce the frequency of application, particularly if you are regularly exposed to sunlight.

Glycolic acid is a potent skincare ingredient with numerous benefits, but it demands careful handling, particularly in relation to sun exposure. Even at low concentrations (e.g. 5%), glycolic acid can still increase photosensitivity due to its exfoliating properties, albeit to a lesser extent than at higher concentrations. Research indicates that it can heighten sensitivity to UV radiation, leading to the formation of sunburn cells and erythema. However, with appropriate precautions such as applying suncream and timing your application, you can still enjoy its benefits whilst minimising the associated risks.

• ANDERSEN F. A. 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. International Journal of Toxicology (1998).

• HONG J. T. & al. Effect of glycolic acid on UVB-induced skin damage and inflammation in guinea pigs. Skin Pharmacology and Applied Skin Physiology (2002).

• KORNHAUSER A. & al. Topical glycolic acid enhances photodamage by ultraviolet light. Photodermatology, Photoimmunology & Photomedicine (2003).

• HEARING V. J. & al. The effects of topically applied glycolic acid and salicylic acid on ultraviolet radiation-induced erythema, DNA damage, and sunburn cell formation in human skin. Journal of Dermatological Science (2009).

• SHARAD J. Glycolic acid peel therapy – A current review. Clinical, Cosmetic and Investigational Dermatology (2013).