Differences Between Salicylic & Glycolic Acids

The use of topical acids to improve the skin's appearance dates back to ancient Egypt, where women bathed in sour milk (lactic acid) to soften sun-dried skin. Today, salicylic and glycolic acids are two of the more commonly used skin-treatment acids, showing effectiveness against wrinkles, hyperpigmentation, and, in particular, acne.

Salicylic Acid

Organic acids are classified as alpha or beta depending on the location of the hydroxy group, the part of the molecule consisting of oxygen and hydrogen. Salicylic acid is a beta-hydroxy acid and can be synthesized in the lab or found naturally in the bark of willow trees. Historical accounts document the use of salicylic acid in face salons as early as the 1900s.

Glycolic Acid

Glycolic acid is an alpha-hydroxy acid that is found naturally in sugar cane and also can be synthesized in the lab. Eugene Van Scott and Ruey Yu pioneered the use of alpha-hydroxy acids in modern skin care. In a 1974 paper, Van Scott reported that a group of fruit acids were highly effective in relieving dryness and normalizing skin in patients with ichthyosis, or disfiguring dry skin. He reasoned that if alpha-hydroxy acids can readily treat this condition, then routine dryness can be treated easily as well.

Mechanism

In 1984, Van Scott and Yu hypothesized that alpha-hydroxy acids work by inhibiting the enzymes that hold dead cells together, allowing for cell renewal. In contrast, salicylic acid is a keratolytic compound that promotes cell renewal by dissolving dead cells.

Skin Treatment

A study in India (published in 2009) compared the effectiveness of glycolic and salicylic-mandelic acids in the treatment of acne. (Mandelic acid is an alpha-hydroxy acid.) The researchers discovered that although both treatments were effective overall against acne, salicyclic-mandelic acid was more effective. They also discovered that both agents led to a subtle decrease in icepick and boxcar scars by stimulating collagen production. Both were also effective against hyperpigmentation, but salicylic acid showed greater success with decreased inflammation as well as a skin whitening effect.

Skin Cancer

As part of research examining whether sun exposure while using glycolic or salicylic acid increased the chances for skin cancer, experiments showed that glycolic acid does not enhance the likelihood of cancer, while salicylic acid actually protects against it.

References

• "NTP Technical Report on the Photocarcinogenesis Study of Glycolic and Salicylic Acid in SKH-1 Mice"; September 2007
• "Glycolic Acid Peels Versus Salicylic-Mandelic Acid Peels in Active Acne Vulgaris and Post-Acne Scarring and Hyperpigmentation: A Comparative Study"; Vijay Kumar Garg, MBBS, MD, MNAMS, et al; Dermatol Surg 2009; 35:59-65
• "Fruit Acids for Fabulous Skin"; Deborah Chase; 1996

Resources

• acne.org