Chemical exfoliation is one of the most transformative steps you can add to your skincare routine. Unlike physical scrubs that can cause micro-tears, chemical exfoliants dissolve the bonds between dead skin cells — revealing smoother, brighter, more even-toned skin underneath.
But with so many acids on the market, the biggest question remains: AHA or BHA — which one do you actually need?
This guide breaks down everything you need to know about alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs), so you can choose the right exfoliant for your skin type and concerns.
Your skin naturally sheds dead cells every 28–40 days. As we age, this process slows down, leading to a buildup of dead skin cells on the surface. The result? Dullness, clogged pores, uneven texture, and hyperpigmentation.
Chemical exfoliants accelerate this shedding process by breaking down the desmosomes — the protein connections that hold dead skin cells together. The two main categories are:
There's also PHA (Polyhydroxy Acids), a gentler cousin with larger molecule sizes, ideal for sensitive skin.
AHAs are water-soluble molecules derived from fruits and milk. They exfoliate the uppermost layer of the skin (stratum corneum) by breaking down the cellular "glue" (desmosomes) that holds dead skin cells together.
| AHA | Source | Molecular Weight | Strength | Best For | |-----|--------|-----------------|----------|----------| | Glycolic Acid | Sugarcane | Smallest | Strongest | Anti-aging, texture | | Lactic Acid | Milk | Medium | Moderate | Dry/sensitive skin, hydration | | Mandelic Acid | Bitter almonds | Large | Gentlest | Acne, sensitive/darker skin | | Tartaric Acid | Grapes | Medium | Moderate | Antioxidant boost | | Citric Acid | Citrus | Medium | Moderate | Brightening, pH adjuster | | Malic Acid | Apples | Medium | Gentle | Mild exfoliation + hydration |
Glycolic acid is the most studied and effective AHA due to its small molecular size (76 Da), which allows deep penetration. Lactic acid is the best choice for dry or sensitive skin because it also acts as a humectant.
BHA (salicylic acid) is oil-soluble, meaning it can penetrate through the lipid (oil) layers of the skin and into the pore itself. This makes it uniquely suited for oily and acne-prone skin.
| Concentration | Use Case | |--------------|----------| | 0.5% | Daily maintenance for mild congestion | | 1–2% | Weekly exfoliation or spot treatment | | 2% | OTC maximum (most common in leave-on products) | | 2–5% | Rinse-off peels and professional treatments | | 10–30% | Professional chemical peels only |
Yes! This is called combination therapy. Popular approaches:
⚠️ Important: Start slow. Don't use both on the same night if you're a beginner. Always follow with SPF.
Week 1–2: Use once or twice weekly, at night only.
Week 3–4: Increase to every other night if no irritation.
Week 5+: Daily use if tolerated (for BHA or gentle AHAs like lactic/mandelic).
| Don't Combine With | Why | |-------------------|-----| | Retinol (same night) | Risk of irritation | | Vitamin C (L-AA, same morning) | Can inactivate each other | | Benzoyl peroxide | Can oxidise and reduce efficacy | | Other exfoliating acids | Excessive irritation |
Yes, but not on the same night if you're a beginner. Alternate nights or use a combination product formulated by a reputable brand.
BHA (salicylic acid) at 2% or less in leave-on products is generally considered safe. AHAs are also safe. Avoid higher concentrations and professional peels.
Most people notice smoother skin within 1–2 weeks. Fading of hyperpigmentation takes 4–8 weeks. Collagen production improvements take 3–6 months.
Yes. BHA in particular can cause a temporary increase in breakouts (purging) as it clears congestion. This typically lasts 2–4 weeks.
Sources: Journal of the American Academy of Dermatology, British Journal of Dermatology, International Journal of Cosmetic Science, Cosmetic Dermatology.
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