AHA vs BHA vs PHA: The Complete Exfoliant Guide

Chemical exfoliants are among the most impactful ingredients you can add to a skincare routine — but the differences between AHAs, BHAs, and PHAs are clinically meaningful, not just marketing distinctions. The wrong choice for your skin type can cause irritation or fail to address your concerns; the right choice can transform skin texture, clarity, and tone within weeks.

AHAs: Alpha-Hydroxy Acids

AHAs are water-soluble acids that work by breaking the bonds between dead skin cells at the skin surface, allowing them to shed more rapidly. The most commonly used AHAs in skincare:

• Glycolic acid — the smallest AHA molecule, deepest penetration, highest potency. Excellent for anti-ageing (stimulates collagen synthesis at higher concentrations), texture refinement, and brightening. The most likely to cause irritation; best for experienced users or those without sensitive skin.
• Lactic acid — larger molecule, more superficial action, gentler than glycolic. Also acts as a humectant, hydrating while it exfoliates. Ideal first AHA for most people. Effective for brightness and texture at 5–10%.
• Mandelic acid — the largest AHA, gentlest, and particularly useful for darker skin tones because it carries a lower risk of post-inflammatory hyperpigmentation than glycolic acid.
• Malic acid and tartaric acid — less commonly used as standalone actives; often found in combination formulas.

AHAs increase UV sensitivity for 24–48 hours after use. Always wear SPF the morning after applying an AHA — and every morning regardless.

BHAs: Beta-Hydroxy Acids

The primary BHA used in skincare is salicylic acid, a naturally occurring compound derived from willow bark. Unlike AHAs, salicylic acid is oil-soluble — meaning it can penetrate through the sebum in pores rather than being limited to the skin surface. This makes it uniquely effective for:

• Clearing blackheads and whiteheads by exfoliating inside the pore lining
• Reducing excess sebum and shine
• Anti-inflammatory effects (salicylic acid is related to aspirin and has demonstrable anti-inflammatory activity at the skin)
• Addressing mild to moderate acne

Effective concentrations range from 0.5% (gentle daily use) to 2% (targeted treatment). BHAs are less likely to cause post-inflammatory hyperpigmentation than AHAs, making them suitable for a broader range of skin tones. Less ideal for dry skin as they can be dehydrating with frequent use.

PHAs: Polyhydroxy Acids

PHAs include gluconolactone, lactobionic acid, and galactose. Their larger molecular size means they penetrate only the very outermost layers of the stratum corneum, delivering exfoliating benefits with significantly reduced irritation. PHAs also have humectant properties and some antioxidant activity. Key attributes:

• Compatible with sensitive and rosacea-prone skin that cannot tolerate AHAs or BHAs
• Gentler than AHAs at equivalent concentrations
• Less dramatically effective for deep texture refinement, but deliver real brightening and smoothing benefits
• Less UV sensitisation than AHAs — though SPF should still be worn daily

Can You Use AHAs and BHAs Together?

Combination AHA/BHA products exist and can be effective — but they carry a higher irritation risk than either acid alone. For most people, using an AHA on some nights and a BHA on others (never the same night as retinol) is a safer and equally effective approach. Beginners should master one acid type before introducing a second.