AHA, BHA and PHA Acids: What They Are, Benefits and How to Choose the Right Type

AHA (Alpha Hydroxy Acid), BHA (Beta Hydroxy Acid) and PHA (Polyhydroxy Acid) are chemical exfoliants widely used in skincare. They help remove old skin cells and reduce clogged pores, making skin look clearer and smoother. However, each type of acid suits a different skin condition, so choosing the right one is very important. In this article, a dermatologist explains the differences, how to choose by skin type, and how to use them safely.

How are AHA, BHA and PHA different?

The main difference is solubility, which determines which layer of skin the acid works on and who it suits.

• AHA (Glycolic Acid, Lactic Acid): Water-soluble acids that work on the top layer of the skin. Suited to dry and dull skin, they help reduce dark marks and make skin smoother.

• BHA (Salicylic Acid): Oil-soluble, so it penetrates deep into pores. Suited to oily skin, blackheads and clogged pores, and it also has anti-inflammatory properties.

• PHA (Gluconolactone, Lactobionic Acid): Larger molecules that absorb more slowly, so they are less irritating than AHA. Suited to sensitive or delicate skin, and they also help the skin retain moisture.

Choosing by skin type

Choosing the right acid and concentration for your skin and experience level reduces the chance of irritation.

• Concentration for beginners: For beginners, suitable concentrations are AHA 4-7% and BHA 0.5-2%.

• Frequency: Use in the evening, starting at 1-3 times a week, then adjust according to how your skin responds.

• Sunscreen is essential: Apply sunscreen SPF 30+ every morning, because these acids make skin more sensitive to sunlight.

Precautions and safe use

• Avoid layering with retinol: Do not use together with retinol on the same night, as this may cause significant irritation. Alternate nights instead.

• Choose the right type of acid: Among AHAs, Glycolic Acid is highly effective but may also be more irritating than Lactic Acid. People with sensitive skin may therefore start with Lactic Acid.

• Stop if irritation is severe: If you have stinging, redness or severe irritation, stop using it and consult a dermatologist.

Frequently asked questions

Should oily, acne-prone skin use AHA or BHA? Oily skin with clogged pores or blackheads suits BHA (Salicylic Acid), because it is oil-soluble and penetrates deep into pores. It also helps reduce inflammation.

Can sensitive skin use exfoliating acids? Yes, but choose PHA, which is less irritating than AHA and helps retain moisture, or start with a low concentration and use it infrequently.

Do I need sunscreen when using exfoliating acids? Absolutely, because the acids make skin more sensitive to sunlight. Apply sunscreen SPF 30+ every morning.

Can I use AHA/BHA together with retinol? They should not be used on the same night as this may cause significant irritation. We recommend alternating nights. If you are unsure, consult a dermatologist.

If you are unsure which exfoliating acid and concentration suit your skin, or you have irritation after using one, consult a dermatologist at Siam Dermatology. Call +66 61 448 7000 or LINE @siamderm

Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed July 16, 2026