Chemical vs Physical Exfoliation
Chemical exfoliants dissolve the protein bonds between corneocytes, allowing orderly shedding. Physical scrubs abrade the surface mechanically — less controlled, higher risk of micro-tears, and increasingly considered outdated by dermatological consensus. Chemical exfoliation, done correctly, is more gentle and more effective.
AHAs: Alpha Hydroxy Acids (Water-Soluble)
AHAs work on the skin's surface, loosening corneocyte adhesion and accelerating desquamation. They are water-soluble, so they cannot penetrate oily follicle linings.
| AHA | Molecule Size | Best For | Effective % |
|---|---|---|---|
| Glycolic Acid | Smallest (76 Da) | Texture, photoageing, dullness | 5–10% |
| Lactic Acid | Medium (90 Da) | Sensitive skin, dry skin, pigmentation | 5–12% |
| Mandelic Acid | Large (152 Da) | Acne-prone, sensitive, darker phototypes | 5–10% |
| Citric Acid | Small (192 Da) | pH adjuster, mild exfoliant | Used as adjuvant |
BHA: Beta Hydroxy Acid (Oil-Soluble)
Salicylic acid (2-hydroxybenzoic acid) is the primary BHA used in skincare. Its oil-solubility is the key distinction: it can penetrate the lipid-rich environment inside hair follicles, dissolving sebum plugs directly. This makes it uniquely effective for:
- Comedonal acne (blackheads, whiteheads)
- Oily skin pore congestion
- Fungal folliculitis (anti-inflammatory, antifungal properties)
Effective concentration: 0.5–2%. FDA-regulated for OTC acne use at 0.5–2%.
PHAs: Polyhydroxy Acids (Gentle, Large-Molecule)
PHAs — gluconolactone, lactobionic acid, galactose — are next-generation exfoliants with larger molecular weights that penetrate more slowly, causing less irritation. They are suitable for:
- Rosacea-prone or sensitive skin needing gentle exfoliation
- Post-retinoid introduction — when barrier is compromised
- Eczema-adjacent skin (with dermatologist guidance)
The pH dependency: AHA exfoliation is pH-dependent — maximum efficacy occurs at pH 3–4. Products above pH 5 have minimal exfoliant activity. Check your product's pH or look for formulations specifically designed for exfoliation, not just containing the acid as a label ingredient.
Frequency Guidelines
| Skin Type | Recommended Frequency |
|---|---|
| Normal/oily skin | 3–4x per week |
| Dry/combination skin | 2–3x per week |
| Sensitive/reactive skin | 1x per week (PHA preferred) |
| Active retinoid user | Reduce to 1–2x per week; alternate nights |
See Skin Cycling for a schedule that coordinates acids with retinoids optimally.