The Bottom Line
Glycolic acid (an AHA) works on the skin surface — best for sun damage, fine lines, dullness, and hyperpigmentation. Salicylic acid (a BHA) penetrates into pores — best for acne, blackheads, and oily skin. Both exfoliate dead skin cells but through different mechanisms and at different depths. Choose based on your primary skin concern, or alternate between them for multiple benefits.
Glycolic Acid (AHA)
- Type: Alpha-hydroxy acid derived from sugarcane
- How it works: Water-soluble, works on the skin surface. Dissolves the bonds between dead skin cells, promoting faster cell turnover.
- Molecule size: The smallest AHA — deepest surface penetration
- Best for: Fine lines, sun damage, dullness, hyperpigmentation, rough texture
- Concentrations: 5-10% for home use, 20-70% for professional peels
- Bonus effects: At higher concentrations, stimulates collagen production in the dermis
- Sun sensitivity: Increases photosensitivity — daily sunscreen is mandatory
Salicylic Acid (BHA)
- Type: Beta-hydroxy acid derived from willow bark
- How it works: Oil-soluble, penetrates INTO pores. Dissolves sebum and dead cells inside follicles.
- Best for: Acne, blackheads, whiteheads, oily skin, enlarged pores
- Concentrations: 0.5-2% for home use, 20-30% for professional peels
- Bonus effects: Anti-inflammatory (related to aspirin) — reduces redness around acne
- Sun sensitivity: Mild increase — sunscreen still important but less photosensitizing than glycolic
Head-to-Head Comparison
| Concern | Winner | Why |
|---|---|---|
| Acne & blackheads | Salicylic acid | Penetrates pores to clear clogs |
| Fine lines & wrinkles | Glycolic acid | Stimulates collagen, smooths surface |
| Dark spots | Glycolic acid | Accelerates pigment turnover |
| Oily skin | Salicylic acid | Dissolves excess oil in pores |
| Dry, dull skin | Glycolic acid | Reveals fresh cells, enhances radiance |
| Sensitive skin | Salicylic acid (or lactic acid) | Anti-inflammatory, less surface irritation |
| Multiple concerns | Both — alternate | Different mechanisms complement each other |
How to Use Each
Glycolic acid: Start at 5% every other night. Increase to nightly, then to 8-10% as tolerated. Use in the evening. Follow with moisturizer. Sunscreen every morning is non-negotiable.
Salicylic acid: Start at 2% every other day. Increase to daily as tolerated. Can be used as a cleanser (shorter contact), toner, or leave-on treatment. Less drying than glycolic for most people.
Alternating both: Glycolic one night, salicylic the next. Or salicylic in the morning (cleanser format), glycolic at night (leave-on). Don't use both on the same application — over-exfoliation risk.
Frequently Asked Questions
Can I use acids with retinol?
Yes, but not on the same night initially. Alternate: retinol one night, acid the next. Once your skin is tolerant (after 4-8 weeks), some people can layer them — acid first, then retinol 30 minutes later. If irritation occurs, stick to alternating.
What about lactic acid?
Lactic acid is a gentler AHA (larger molecule, less penetrating). It's ideal for sensitive skin or AHA beginners. It also has humectant properties (attracts water), making it less drying. Think of it as glycolic acid's gentler sibling.
How do I know if I'm over-exfoliating?
Signs: increased redness, stinging with products that were previously fine, excessive dryness or flaking, skin that looks shiny/raw rather than healthy/glowing. If this happens, stop all acids for 1-2 weeks and focus on gentle cleansing and ceramide moisturizer until your barrier recovers.
- Tang SC, Yang JH. "Dual effects of alpha-hydroxy acids on the skin." Molecules. 2018;23(4):863.
- Arif T. "Salicylic acid as a peeling agent." Clinical, Cosmetic and Investigational Dermatology. 2015;8:455-461.
- Kornhauser A, et al. "Applications of hydroxy acids." Clinical, Cosmetic and Investigational Dermatology. 2010;3:135-142.