An AHA peel is a chemical exfoliation treatment that uses alpha hydroxy acids to dissolve the bonds holding dead skin cells together, revealing fresher skin underneath. AHA peels come in a wide range of strengths: over-the-counter products contain up to 10% acid, salon treatments use up to 30%, and medical-grade peels go as high as 70%. The strength you use determines how deep the peel penetrates and how dramatic the results will be.
How AHA Peels Work on Your Skin
Your outer layer of skin is made up of cells held together by protein structures called desmosomes, which act like tiny rivets between cells. Alpha hydroxy acids lower the pH of the skin’s surface, which disrupts the ionic bonds in these structures and essentially loosens the glue keeping dead cells attached. This triggers desquamation, the natural shedding process that your skin performs on its own but much more slowly.
Once that top layer starts to come off, your skin responds by ramping up cell turnover. New cells move to the surface faster, and superficial peels also stimulate collagen production in the deeper layers. After a superficial AHA peel, the skin typically regenerates within 3 to 5 days, with visible flaking that’s generally mild and manageable.
Common Types of AHAs
Not all alpha hydroxy acids are the same. Their molecular size determines how quickly and deeply they penetrate the skin, which affects both results and irritation.
- Glycolic acid is derived from sugar cane and has the smallest, simplest molecular structure of any AHA. That small size lets it penetrate quickly, making it the most potent option for surface-level exfoliation. Professional peels typically use concentrations of 20 to 50%, while 70% formulas enter medium-depth territory.
- Lactic acid is structurally similar to glycolic acid but slightly larger, so it penetrates a bit more gently. Professional peels usually range from 10 to 30%. Skin reepithelialization (the formation of new surface skin) takes about 7 to 10 days at higher concentrations.
- Mandelic acid has a much larger molecular structure with a benzene ring attached, which means it penetrates the skin more slowly and evenly. This makes it the gentlest of the three and suitable for sensitive or darker skin tones that are more prone to post-inflammatory pigmentation. Recovery after a mandelic peel is often complete within 3 to 5 days.
Lactic and mandelic acid peels have gained popularity as alternatives to glycolic acid because they offer comparable effectiveness with less discomfort and minimal downtime.
What AHA Peels Treat
AHA peels are used for smoothing fine lines and surface wrinkles, improving skin texture and tone, unclogging pores, and addressing uneven pigmentation. The superficial versions are best suited for mild concerns: dull skin, rough texture, light acne marks, and early sun damage. They won’t reach deep wrinkles or severe scarring, which require medium or deep peels performed by dermatologists.
For conditions like melasma or post-acne dark spots, a series of peels spaced several weeks apart typically produces better results than a single session. The combination of accelerated cell turnover and increased collagen production gradually evens out skin tone and improves firmness over multiple treatments.
Concentration and pH Matter More Than You Think
Two AHA products can list the same percentage on the label and deliver very different results. That’s because what actually exfoliates your skin is the “free acid,” the portion of acid that’s active and unneutralized. The amount of free acid depends on the product’s pH. A lower pH means more of the acid is in its active form and available to work on the skin. A higher pH means less free acid, even at the same listed concentration.
This is why regulators set limits on both concentration and pH together. The U.S. FDA, working with the Cosmetic Ingredient Review panel, considers AHA products safe for consumer use when the concentration is 10% or less and the pH is 3.5 or greater. The product should also either protect against increased sun sensitivity or include directions for daily sun protection. For salon use, concentrations up to 30% with a pH as low as 3 are considered appropriate when applied by trained professionals. Anything stronger falls into the medical category.
European regulations are stricter. The EU’s scientific committee has recommended that glycolic acid in cosmetics stay at 4% or below with a pH of at least 3.8, and lactic acid at 2.5% or below with a pH of at least 5.
Sun Sensitivity After a Peel
AHA peels increase your skin’s sensitivity to UV radiation, and this isn’t just a temporary effect that fades when redness goes away. You should apply broad-spectrum SPF 30 or higher every day during a course of peels and for at least six weeks after your last treatment. If you have very fair skin or are prone to pigmentation issues, SPF 50 is a better choice. This applies regardless of the weather or season.
This photosensitivity is one of the biggest practical considerations with AHA peels. Ingredients that exfoliate or accelerate cell turnover are the primary culprits behind increased sun vulnerability, and AHAs are no exception. If you’re also using retinol or hydroquinone in your routine, your skin is even more susceptible, and sun protection becomes non-negotiable.
Purging Versus a Bad Reaction
It’s common to experience some breakouts after starting AHA peels, especially if you’re acne-prone. This is called purging, and it happens because the accelerated cell turnover pushes clogged pores to the surface faster than they would on their own. Purging breakouts tend to appear in small clusters in areas where you normally get acne, and they should resolve within a few weeks.
An allergic reaction or irritant response looks different. Severe redness, itching, swelling, or a rash that spreads to areas where you don’t typically break out suggests your skin isn’t tolerating the product. If the reaction is intense, stop using the peel. If breakouts persist beyond a few weeks or you’re unsure which you’re experiencing, a dermatologist can help you distinguish between the two.
What to Expect During and After Treatment
At-home AHA peels at 10% or below are straightforward. You apply the product, leave it on for the directed time (usually a few minutes), and rinse. You may feel tingling or mild warmth, which is normal. Professional peels at higher concentrations involve a trained esthetician or dermatologist monitoring your skin’s response and neutralizing the acid at the right moment. The higher the concentration, the more important this timing becomes.
After a superficial peel, expect mild flaking and slight tightness for 3 to 5 days as your skin regenerates. Your skin may look pink or feel sensitive during this window. Avoid other exfoliating products, direct sun exposure, and heavy makeup while you’re peeling. Most people can return to their normal routine within a week. Results build over time with repeated treatments, as each session removes another layer of damaged cells and stimulates fresh collagen beneath the surface.
Who Should Avoid AHA Peels
AHA peels aren’t a good fit if you have active sunburn, open wounds, or inflamed skin conditions like eczema flares in the treatment area. If you’re using prescription retinoids, the combination can cause excessive irritation and barrier damage, so you’ll typically need to pause them before and after a peel. The same goes for other prescription topicals like antibiotic or antifungal creams, which can also increase photosensitivity and compound the skin-thinning effect.
People with darker skin tones should approach higher-concentration peels with caution, as aggressive exfoliation can trigger post-inflammatory hyperpigmentation. Mandelic acid peels are often the preferred choice in this case because of their slower, more uniform penetration. Starting at a lower concentration and gradually increasing gives your skin time to adapt and reduces the risk of overcorrection.