Medical disclaimer: This page is informational only and does not constitute medical advice, diagnosis, or treatment. Consult a board-certified dermatologist before starting any active ingredient.
Photosensitivity warning: This ingredient increases skin sensitivity to UV radiation. Daily broad-spectrum SPF 30+ sunscreen is required during treatment. Avoid prolonged sun exposure.
Reviewer status: Pending board-certified dermatologist review. Content reviewed for factual accuracy by editorial staff only.
Comparison Guide
AHA vs BHA vs PHA
Chemical exfoliants work by dissolving the bonds that hold dead skin cells together. The three families (AHA, BHA, PHA) share this mechanism but differ in where they work, how fast, and for which skin types. Picking the wrong one means exfoliating where you do not need it.
Side-by-Side Comparison
| Feature | AHA | BHA | PHA |
|---|---|---|---|
| Mechanism | Surface exfoliation (dissolves corneocyte bonds) | Follicular penetration (oil-soluble) | Surface exfoliation (slower, gentler) |
| Primary examples | Glycolic acid, lactic acid, mandelic acid | Salicylic acid | Gluconolactone, lactobionic acid |
| Best for | Dry skin, fine lines, surface texture | Oily, acne-prone, blackheads | Sensitive skin, rosacea-prone |
| Irritation level | Moderate (glycolic > lactic > mandelic) | Low-moderate | Low |
| Sun sensitivity | Yes — SPF required | Yes — SPF required | Mild — SPF recommended |
| Pregnancy safety | Lactic acid: generally low-risk | Avoid (consult OB-GYN) | Generally low-risk |
| pH for efficacy | 3.5-4.5 | 3.0-4.0 | 3.5-5.5 |
Sources: Decker and Graber 2012; Green 2009; AAD chemical exfoliant guidelines.
Which Exfoliant for Which Skin Type
Dry or normal skin with fine lines
AHA (glycolic or lactic acid)
Surface exfoliation speeds cell turnover and improves texture faster than BHAs, with no oil-penetration benefit needed
Oily, acne-prone, or blackhead-prone skin
BHA (salicylic acid 2%)
Oil-solubility penetrates follicles to dissolve sebum plugs — the only exfoliant that works inside pores
Sensitive, reactive, or rosacea-prone skin
PHA (gluconolactone)
Larger molecular size means slower penetration and less irritation than glycolic acid; comparable efficacy with fewer side effects
Combination skin (oily T-zone, dry cheeks)
BHA + lactic acid (different zones or alternating)
BHA for the T-zone comedones; lactic acid for dry areas needing surface hydration and exfoliation
Sensitive skin new to exfoliants
Lactic acid or mandelic acid (start)
Larger molecules = slower penetration = lower chance of initial irritation; build tolerance then consider stronger AHAs
Frequently Asked Questions
What is the difference between AHA and BHA?
AHAs (alpha hydroxy acids) are water-soluble and work primarily on the skin surface to dissolve the bonds between dead skin cells. Examples: glycolic acid, lactic acid, mandelic acid. BHAs (beta hydroxy acids) are oil-soluble and penetrate into sebum-filled follicles. The primary BHA in skincare is salicylic acid. AHAs improve surface texture, fine lines, and dry skin. BHAs address clogged pores, blackheads, and oily/acne-prone skin.
What is PHA and how is it different from AHA?
PHAs (polyhydroxy acids) include gluconolactone, lactobionic acid, and maltobionic acid. They are AHAs with a larger molecular structure that penetrates skin more slowly, producing less irritation and sensitivity. PHAs are suitable for very sensitive skin, rosacea-prone skin, or people who cannot tolerate glycolic or lactic acid. Clinical data shows comparable efficacy to AHAs with significantly lower irritation rates. (Source: Green 2009, J. Clin. Aesthet. Dermatol.)
Can I use AHA and BHA together?
Yes. AHAs and BHAs have complementary mechanisms — surface exfoliation and follicular clearing. Many products combine them. If using separately, apply at the same step or at different times to avoid over-exfoliation. Daily use of both together can cause dryness and barrier disruption in sensitive skin; start with 2-3 times per week and increase as tolerated.
Which AHA is gentlest?
Lactic acid is generally considered gentler than glycolic acid due to its larger molecular size (slower penetration) and humectant properties. Mandelic acid has an even larger molecule and is often recommended for sensitive skin or first-time AHA users. PHAs (gluconolactone) are gentler than all AHAs for most skin types.
Do chemical exfoliants cause sun sensitivity?
Yes. AHAs and BHAs increase UV sensitivity for up to 7 days after use. Daily broad-spectrum SPF 30+ is required when using chemical exfoliants. This does not mean you cannot use them — it means SPF is non-optional when you do. PHAs cause less sun sensitivity than glycolic or lactic acid, but SPF is still recommended.