Hydroxy Acids

Hydroxy acids occur naturally in fruits, milk and sugar cane. The three types of hydroxy acids used in skin care products are alpha hydroxy acid (AHA), beta hydroxy acid (BHA) and polyhydroxy acid (PHA). These acids may be natural or synthetic.

Alpha Hydroxy Acid (AHA) Products

AHAs may decrease the signs of aging, making the skin smoother by exfoliating dead skin cells. AHAs may also stimulate production of collagen and elastin in the skin. Types of alpha hydroxy acid include:

  • Citric acid (from oranges and lemons)
  • Glycolic acid (from sugar)
  • Lactic acid (from milk)
  • Malic acid (from apples and pears)
  • Tartaric acid (from grapes).

Most alpha hydroxy acid products contain glycolic acid. Over-the-counter products contain a glycolic acid concentration of between 2 to 10 percent. For at-home treatments, higher concentration alpha hydroxy acid products may be more effective than those with lower concentrations. Prescription glycolic acid products contain at least 12 percent glycolic acid, while glycolic acid peels done in a doctor’s office contain 30 to 70 percent acid.

Potential side effects from alpha hydroxy acid products include burning, itching, pain, scarring and sun sensitivity. When using hydroxy acids, always wear sun protection or avoid sunlight.

Beta Hydroxy Acids

The main difference between alpha hydroxy acid and beta hydroxy acid is that AHAs are water-soluble and BHAs are oil-soluble. BHAs can better penetrate pores and are often used to treat acne. The most commonly used BHA in skin care products is salicylic acid. Other beta hydroxy acids include:

  • Beta hydroxybutanoic acid
  • Trethocanic acid
  • Tropic acid.

BHA products have the same potential side effects as AHA products. Also, salicylic acid is an ingredient of aspirin, so make sure to avoid salicylic acid products if you’re allergic to aspirin. Pregnant women also need to avoid products with high concentrations of BHAs. The small amounts of salicylic acid found in a facial cleanser aren’t likely to cause problems, but chemical peels containing salicylic acid may not be safe. If you’re pregnant, talk to your doctor before getting a chemical peel or using salicylic acid products.

Polyhydroxy Acids

PHAs are relatively new on the skin care scene. While similar to AHAs, they have a larger molecular structure. Some research suggests that PHA products–such as gluconolactone and lactobionic acid–may irritate the skin less than beta or alpha hydroxy acid products do.

The choice of hydroxy acid products can be overwhelming. If you aren’t sure what’s best for you, consult your dermatologist.


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