AHA vs PHA: which chemical exfoliant is right for your skin type?

A clear breakdown of AHA versus PHA chemical exfoliants, how each one works, and which may suit sensitive, dry, or reactive skin types better

AHA (alpha hydroxy acid) and PHA (polyhydroxy acid) are two families of chemical exfoliants that dissolve dead skin cells without the micro-tears caused by physical scrubs, but they differ in molecule size, penetration depth, and irritation potential -- making AHAs better suited for normal-to-dry skin and PHAs the safer pick for sensitive or reactive skin ¹².

Key takeaways

• AHAs like glycolic and lactic acid work on the skin's surface to brighten tone, smooth texture, and reduce fine lines ¹³.
• PHAs such as gluconolactone have larger molecules that exfoliate gently, add moisture, and skip the photosensitivity risk that comes with AHAs ²⁴.
• Your skin type -- not marketing hype -- should determine which acid you reach for ¹².
• Both families increase cell turnover, but PHAs also strengthen your moisture barrier while they work ².
• Always patch test a new exfoliant on your inner arm and wear SPF daily when using AHAs ¹.

What do chemical exfoliants actually do to your skin?

Chemical exfoliants loosen the bonds between dead cells on the surface of your stratum corneum (the outermost layer of skin). Instead of scrubbing them away physically, the acid dissolves the "glue" so those cells shed on their own schedule. The result is smoother texture, more even tone, and better absorption of everything you layer afterward ¹.

This matters because physical scrubs can create tiny tears in already-irritated skin. If you have spent a summer in the sun or you deal with rosacea or eczema, the last thing your face needs is abrasion. A well-chosen chemical exfoliant does the same job with less collateral damage ³.

How are AHAs and PHAs different?

The fundamental difference is molecule size. AHAs are small, water-soluble molecules that penetrate into the upper layers of the epidermis. PHAs are structurally similar but significantly larger, so they sit closer to the surface and work more slowly ².

That size gap creates a cascade of practical differences.

Clinical comparison studies have shown that PHA regimens deliver anti-aging results comparable to AHA regimens, but with significantly less stinging and burning at both the 6-week and 12-week marks ⁵.

Which AHAs should you know about?

Three AHAs dominate the skincare aisle, and each has a distinct personality.

Glycolic acid has the smallest molecule of the group, so it penetrates deepest and delivers the most visible results the fastest. It is the workhorse of professional-grade peels and has decades of clinical data behind it ¹³. The tradeoff: it is also the most likely to irritate, especially on compromised skin.

Lactic acid is one step gentler. Research comparing the two at equivalent concentrations found that lactic acid produced similar improvements in hydration and wrinkle depth with fewer consumer complaints of irritation ³. It also acts as a mild humectant, which means it pulls water into the skin while it exfoliates.

Mandelic acid has the largest AHA molecule. It penetrates slowly, making it a good starting point if you have never used acids before or if your skin tends toward reactive.

Both glycolic and lactic acid have been shown to suppress melanin production by inhibiting tyrosinase activity, which is why they are so popular for addressing uneven pigmentation and dark spots ³.

What makes PHAs unique?

PHAs were specifically engineered to deliver exfoliation benefits to skin that cannot tolerate traditional AHAs. The two you will encounter most often are gluconolactone and lactobionic acid ².

Their larger molecular structure means three things for your skin. First, they cannot penetrate as deeply, so the risk of irritation drops dramatically. Second, they attract and hold water thanks to multiple hydroxyl groups, functioning as humectants on top of being exfoliants. Third, they do not increase your skin's sensitivity to UV the way AHAs do ²⁴.

Gluconolactone also chelates (binds to) metal ions and may scavenge free radicals, giving it antioxidant properties that AHAs lack ⁴. Clinical data confirms that PHAs are compatible with rosacea, atopic dermatitis, and post-procedure skin ².

If your skin stings when you apply your current exfoliant, a PHA is worth trying.

Can you use AHAs and PHAs together?

Yes, but start carefully. Some people alternate them -- an AHA on resilient days, a PHA when skin feels reactive. Others use a PHA daily and reserve AHAs for a once-weekly treatment.

The important thing is to avoid stacking multiple exfoliants in the same routine step. More acid does not mean faster results. Over-exfoliation weakens your moisture barrier, increases sensitivity, and slows healing ¹⁶.

A simple approach: use one exfoliant 2-3 times per week and monitor how your skin responds for at least two weeks before adding intensity.

How should you pick based on your skin type?

Dry skin: Start with lactic acid (5-10%). It exfoliates and hydrates simultaneously. If you want something even gentler, lactobionic acid (a PHA) is a strong alternative.

Oily or congested skin: Glycolic acid (5-10%) works well for surface texture and dullness. For deeper pore congestion, you might combine it with a BHA (salicylic acid) on alternating nights -- but that is a separate conversation.

Sensitive or rosacea-prone skin: PHAs are your safest entry point. Gluconolactone at 4-10% provides exfoliation with minimal risk of flare-ups ². If your skin is currently compromised, start at the lower end.

Post-summer skin: Your barrier may be weakened from UV exposure. Begin with a PHA for 2-3 weeks, then graduate to a mild AHA if your skin tolerates it ²⁵.

The Skin Bliss Ingredient Compatibility Checker can flag potential clashes if you are layering an exfoliant with other actives like retinol or vitamin C, so you avoid overloading your routine.

What mistakes should you avoid with chemical exfoliants?

Using too high a concentration too soon. A 30% glycolic peel is not a good first exfoliant. Start low (5-8% for AHAs, 4-10% for PHAs) and increase over weeks.

Skipping SPF with AHAs. AHAs increase photosensitivity. If you use glycolic or lactic acid and skip sunscreen, you are undoing the work and risking hyperpigmentation. Apply broad-spectrum SPF 30+ every morning and reapply every two hours in direct sun ¹.

Exfoliating daily. Your skin needs time between sessions to rebuild. Two to three times per week is plenty for most people ⁶.

Mixing too many actives. Using an AHA alongside retinol and vitamin C in the same PM routine is a recipe for barrier damage. Space your actives across different nights.

FAQ

Can I use AHAs if I have sensitive skin?
You can, but proceed with caution. Lactic acid and mandelic acid are the most tolerable AHAs for reactive skin because of their larger molecule sizes ³. Start at low concentrations (5%), apply every third day, and always patch test on your inner arm first. If even mild AHAs irritate, switch to a PHA.

Do PHAs work as well as AHAs for anti-aging?
Clinical studies show that PHA regimens deliver comparable anti-aging improvements to AHA regimens, including reduced fine lines and improved firmness, while causing significantly less irritation ⁵. The results may take slightly longer to appear because PHAs work more gradually.

Should I use chemical exfoliants in the morning or at night?
Night is generally better, especially for AHAs. Your skin repairs itself during sleep, and applying an AHA at night avoids immediate UV exposure. PHAs can technically be used morning or night since they do not increase photosensitivity, but nighttime application still maximizes the exfoliation window ²⁴.

How long until I see results?
Expect initial texture improvements within 2-3 weeks. Meaningful changes in tone, fine lines, and hyperpigmentation typically take 6-12 weeks of consistent use ¹.

Can I use a chemical exfoliant after a sunburn?
No. Wait until your skin is fully healed -- no redness, no peeling, no tenderness. Applying acid to compromised skin worsens inflammation and delays recovery. Focus on gentle hydration and barrier repair first, then reintroduce exfoliation gradually.