Q: Should AHA, BHA, and PHA acids be applied to dry or damp skin?

All keratolytics (which, in fact, include not only AHA/BHA/PHA but also urea and acids from other groups like azelaic acid) are recommended to be applied to dry skin. Why? It’s assumed that damp skin naturally acts as a conductor for actives. Acids that work on the surface don’t need to “dive deep” – this can cause excessive skin irritation without providing any additional benefits.

Cosmetic chemist and founder of Chemist Corner, Perry Romanowski, answered why The Ordinary recommends applying their AHA 30% + BHA 2% Peeling Solution to dry rather than damp skin: “Using it on a wet surface would dilute the acid so it might not be as effective. There may be an exothermic reaction if you put the product on wet skin that some people might find to be a burning sensation.”

Why Apply Acids to Dry Skin?

  1. Effectiveness: When acids are applied to dry skin, they remain concentrated and can work more effectively on the surface. This ensures they can perform their exfoliating actions without being diluted.
  2. Irritation: Applying acids to damp skin can increase the risk of irritation. Damp skin enhances the penetration of actives, which can lead to deeper penetration than necessary for surface-exfoliating acids, potentially causing more irritation without added benefit.

In conclusion, for most keratolytic treatments, applying to dry skin is the recommended method to ensure effectiveness while minimizing the risk of irritation.


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