AHA vs BHA vs PHA: Which Exfoliant Is Right for You?
Alpha hydroxy acids, beta hydroxy acids, and polyhydroxy acids each exfoliate differently. Learn which chemical exfoliant matches your skin type and anti-aging goals.
AHA vs BHA vs PHA: A Complete Guide to Chemical Exfoliants
Chemical exfoliation is one of the most effective strategies for combating the visible signs of aging. Unlike physical scrubs that rely on abrasive particles, chemical exfoliants use acids to dissolve the bonds between dead skin cells, encouraging their removal and revealing fresher, smoother skin beneath.
The three main categories of chemical exfoliants — AHAs, BHAs, and PHAs — each have unique properties that make them suited to different skin types and concerns. Understanding these differences is the key to choosing the right exfoliant for your skin.
Alpha Hydroxy Acids (AHAs)
AHAs are water-soluble acids derived from natural sources such as sugarcane, milk, and fruit. They work primarily on the skin's surface, dissolving the intercellular "glue" that holds dead cells together in the outermost layer of the epidermis.
Common AHAs
- Glycolic acid (from sugarcane) — smallest molecule, deepest penetration, most potent
- Lactic acid (from milk) — slightly larger molecule, gentler, also provides hydration
- Mandelic acid (from almonds) — larger molecule, gentlest AHA, better for sensitive and darker skin tones
- Tartaric acid (from grapes)
- Citric acid (from citrus fruits)
- Malic acid (from apples)
What AHAs Do Best
- Smooth rough texture and reduce flakiness
- Brighten dull, uneven skin tone
- Fade hyperpigmentation and age spots
- Reduce the appearance of fine lines
- Improve the penetration of other skincare products
- Stimulate collagen production with consistent use
AHA Considerations
AHAs increase sun sensitivity (photosensitivity), making daily SPF application essential. They can cause stinging, redness, and peeling, particularly at higher concentrations. Most people tolerate 5% to 10% glycolic acid well for daily use, while higher concentrations (20% to 70%) are reserved for professional peels.
Beta Hydroxy Acids (BHAs)
The primary BHA used in skincare is salicylic acid, a lipid-soluble (oil-soluble) acid derived from willow bark. Unlike water-soluble AHAs, BHA can penetrate into the pores through the oily sebum that lines them, making it uniquely effective for treating congested and acne-prone skin.
How BHA Works Differently
BHA's oil solubility allows it to work both on the skin's surface and inside the pore lining. This dual action makes it especially effective at:
- Unclogging pores and dissolving blackheads and whiteheads
- Reducing excess oil production
- Calming inflammation and redness
- Exfoliating the skin's surface (though more gently than most AHAs)
- Providing mild antibacterial effects
What BHA Does Best
- Treats and prevents acne breakouts
- Minimizes pore appearance
- Controls oiliness
- Reduces redness and inflammation
- Exfoliates without as much surface irritation as AHAs
- Works for body acne and keratosis pilaris
BHA Considerations
BHA is generally well-tolerated and less likely to cause the stinging and redness associated with AHAs. The standard concentration in over-the-counter products is 0.5% to 2% salicylic acid. While BHA does increase some photosensitivity, the effect is less pronounced than with AHAs. Those with aspirin allergies should consult a physician before using salicylic acid.
Polyhydroxy Acids (PHAs)
PHAs are the newest and gentlest generation of chemical exfoliants. They include gluconolactone, lactobionic acid, and galactose. Their molecular structure is significantly larger than AHAs and BHAs, which means they cannot penetrate as deeply into the skin — but this is precisely what makes them ideal for sensitive, reactive, or compromised skin.
How PHAs Are Different
- Larger molecules penetrate more slowly, reducing irritation
- Humectant properties attract and bind moisture, providing hydration while exfoliating
- Antioxidant activity offers additional protection against free radical damage
- Less photosensitizing than AHAs, though sun protection is still recommended
- Compatible with most skin conditions, including rosacea and eczema
What PHAs Do Best
- Gently exfoliate without causing irritation or barrier disruption
- Hydrate while exfoliating (dual-action benefit)
- Improve skin texture for those who cannot tolerate AHAs or BHAs
- Provide antioxidant protection
- Work safely alongside retinoids and other actives
- Serve as a gateway exfoliant for skincare beginners
PHA Considerations
Because PHAs work on the outermost surface and do not penetrate deeply, their exfoliating effects are milder than AHAs. Those seeking significant improvement in deep wrinkles, pronounced hyperpigmentation, or severe textural irregularities may need to graduate to AHAs once their skin builds tolerance.
Triple Comparison
| Feature | AHA | BHA | PHA |
|---|---|---|---|
| Solubility | Water-soluble | Oil-soluble | Water-soluble |
| Penetration depth | Surface to moderate | Surface and inside pores | Surface only |
| Best for | Dullness, fine lines, pigmentation | Acne, oiliness, clogged pores | Sensitive skin, hydration |
| Exfoliation intensity | Moderate to strong | Moderate | Gentle |
| Hydrating | Lactic acid only | No | Yes (humectant properties) |
| Anti-inflammatory | Minimal | Yes | Moderate |
| Photosensitivity | Significant | Mild | Minimal |
| Suitable for sensitive skin | Depends on type/concentration | Generally yes | Excellent |
| Suitable for acne-prone skin | Yes (can exacerbate in some) | Excellent | Yes |
| Suitable for dry skin | Lactic and mandelic acid | Less ideal | Excellent |
| Typical concentration | 5–10% daily; up to 70% professional | 0.5–2% | 5–15% |
Choosing by Skin Type
Oily and Acne-Prone Skin
Best choice: BHA (salicylic acid)
BHA's oil solubility makes it uniquely suited to penetrate congested pores and dissolve the sebum and debris that cause breakouts. Its anti-inflammatory properties also calm the redness associated with active acne.
Dry and Sun-Damaged Skin
Best choice: AHA (glycolic or lactic acid)
AHAs dissolve the buildup of dry, dead surface cells that make skin look dull and flaky. Lactic acid offers the additional benefit of humectant properties, drawing moisture into the skin while exfoliating.
Sensitive and Reactive Skin
Best choice: PHA (gluconolactone or lactobionic acid)
PHAs deliver gentle exfoliation without disrupting the skin barrier or causing significant irritation. Their hydrating and antioxidant properties make them ideal for rosacea-prone skin or anyone who has previously reacted to AHAs.
Combination Skin
Best choice: BHA or a combination product
If you have an oily T-zone but dry cheeks, BHA works well overall due to its pore-clearing ability and gentler surface exfoliation. Alternatively, some formulations combine BHA with a mild AHA for balanced results.
Mature and Aging Skin
Best choice: AHA (glycolic acid) or AHA + PHA combination
Glycolic acid's ability to stimulate collagen, smooth texture, and fade age spots makes it the most effective exfoliant for addressing multiple signs of aging. Adding a PHA product provides additional hydration and antioxidant support.
Can You Combine AHAs, BHAs, and PHAs?
Yes, but with caution. Over-exfoliation is one of the most common skincare mistakes, leading to a compromised skin barrier, increased sensitivity, redness, and breakouts.
Safe Combination Strategies
- Alternate days: Use BHA one day and AHA the next
- Different times: BHA in the morning, AHA in the evening
- Multi-acid products: Choose well-formulated products that combine acids at balanced concentrations
- Avoid combining high-concentration products from different categories in the same routine
Signs of Over-Exfoliation
- Persistent tightness, stinging, or burning
- Unusual redness or sensitivity
- Increased breakouts
- Shiny, waxy-looking skin
- Flaking that worsens rather than improves
If you notice these signs, stop all exfoliating products for 1 to 2 weeks and focus on hydration and barrier repair.
The Bottom Line
AHAs, BHAs, and PHAs each excel in different areas. AHAs are the workhorses of anti-aging exfoliation, delivering brightening, smoothing, and collagen-stimulating benefits. BHAs are the go-to for oil control and pore management. PHAs are the gentle all-rounders, providing exfoliation with built-in hydration for even the most reactive skin.
The right exfoliant depends on your skin type, primary concerns, and tolerance for active ingredients. Start with a low concentration, introduce gradually, and always pair chemical exfoliation with diligent sun protection. When in doubt, a dermatologist can help you select the optimal acid — or combination of acids — for your skin.
