Skincare acids are some of the most effective ingredients available — and also some of the most confusing. Glycolic, lactic, salicylic, mandelic, azelaic — the list is long and the differences matter. Using the wrong acid for your skin type, or using it incorrectly, can cause more irritation than progress.
This guide breaks down exactly how each category works, who it's for, and how to use it without damaging your skin.
The Three Main Categories
AHAs — Alpha Hydroxy Acids
AHAs are water-soluble acids that exfoliate the skin's surface by dissolving the bonds holding dead skin cells together. They work at the top layers of the skin, making them effective for texture, dullness, hyperpigmentation, and fine lines.
Glycolic Acid — The smallest AHA molecule, which means it penetrates the deepest and works the fastest — but also causes the most irritation. Effective for significant resurfacing, texture improvement, and addressing photodamage. Best for normal to oily skin that's not sensitive or reactive. PCA Skin Resurfacing Serum ($113) is our most potent glycolic option.
Lactic Acid — Larger molecule than glycolic, so it absorbs more slowly and is significantly gentler. Also a humectant, meaning it hydrates while it exfoliates — making it unusually well-suited to dry and sensitive skin. Addresses texture and hyperpigmentation with less risk of irritation. Found in Face Reality Glycolic-Lactic Toner ($33) and PCA Skin Smoothing Toner ($48).
Mandelic Acid — The largest and gentlest AHA — slow absorption means it works gradually and consistently without the irritation spike of glycolic. Has mild antibacterial properties that make it particularly valuable for acne-prone skin, and it's the best AHA for deeper skin tones prone to post-inflammatory hyperpigmentation. Face Reality Mandelic Serum ($42–$48) is available in multiple strengths and is one of our most recommended acids for acne-prone and sensitive skin tones. It's also one of the few exfoliating acids considered safe during pregnancy and breastfeeding — see our full pregnancy & breastfeeding safe skincare collection for more.
Best AHA for:
- Resurfacing and photodamage → glycolic
- Dry or sensitive skin → lactic
- Acne-prone or darker skin tones → mandelic
BHAs — Beta Hydroxy Acids
BHAs are oil-soluble acids, which means they can penetrate into the pore lining — something water-soluble AHAs cannot do. This makes them uniquely effective for oily skin, blackheads, and acne-prone skin where the congestion lives inside the pore itself.
Salicylic Acid — The primary BHA used in skincare. At concentrations of 0.5–2%, it dissolves the sebum and dead cell buildup inside pores, making it the most effective OTC ingredient for blackheads, whiteheads, and acne congestion. It's also anti-inflammatory, which helps calm the redness around active breakouts. Note: high-concentration leave-on salicylic acid is generally avoided during pregnancy — mandelic acid is a safe alternative that provides similar exfoliation without the same concerns.
Best-used BHA products at Cleanse:
- Skin Script Raspberry Refining Cleanser — $33 (daily BHA cleanser)
- Face Reality Sal-C Toner — $31 (BHA toning step with vitamin C)
- Face Reality Moisture Balance Toner — $34 (salicylic acid toner for AM use)
Best BHA for: Oily skin, blackheads, acne, congested pores
PHAs — Polyhydroxy Acids
PHAs are the newest generation of exfoliating acids — larger molecules than AHAs, which means the slowest, most superficial penetration and virtually no irritation. They're not as potent as glycolic or even lactic acid, but they're appropriate for skin that can't tolerate traditional AHAs at all — rosacea, post-treatment skin, extreme sensitivity.
PHAs also have antioxidant properties and support skin barrier function, making them a useful choice for anyone whose barrier has been compromised by over-exfoliation or harsh treatment.
Best PHA for: Rosacea, extreme sensitivity, post-procedure, barrier recovery
AHA vs. BHA vs. PHA: Quick Reference
| AHA | BHA | PHA | |
|---|---|---|---|
| Solubility | Water-soluble | Oil-soluble | Water-soluble |
| Penetration | Surface | Into pore | Very surface |
| Best for | Texture, tone, dullness | Blackheads, acne, oily | Sensitivity, barrier repair |
| Irritation potential | Moderate | Low–moderate | Very low |
| Pregnancy safe | Most types (mandelic, lactic) | Avoid high concentrations | Generally yes |
How to Use Acids Safely
Start low and slow. Begin with 1–2x per week and work up to the frequency your skin tolerates. Don't start with the highest-strength product available — build to it over weeks.
Apply to dry skin. Wet skin speeds absorption of acids and increases the chance of irritation. Wait 5–10 minutes after cleansing or toning before applying an active acid serum.
Don't mix multiple acids in the same session. Using a glycolic toner, a BHA serum, and an AHA exfoliating pad on the same evening is too much. Choose one acid treatment per session.
Always use SPF the next morning. AHAs and BHAs increase photosensitivity by removing the dead surface layer that partially absorbs UV. SkinBetter ToneSmart SPF 75 ($75) is our top recommendation for daily protection alongside acid use.
Watch for the right kind of response. A slight tingle is normal, especially with glycolic. Burning, stinging that doesn't subside, redness that persists for hours, or peeling and flaking after every use are signs you're over-exfoliating. Scale back or switch to a gentler acid.
If your skin needs extra reinforcement while introducing acids, SIV Biome Balancing Serum is a good layering option for calming reactive or barrier-compromised skin between acid treatments.
Not sure which acid is right for your skin? Contact our team — we help clients choose the right active ingredients for their specific concerns every day.
— Lisa, Co-Founder, Licensed Esthetician & RN at Cleanse Face & Body Bar