AHA, BHA, and PHA Exfoliants: Choose the Right Acid for Your Skin

Chemical exfoliants fall into three categories—alpha hydroxy acids (AHA), beta hydroxy acids (BHA), and polyhydroxy acids (PHA)—each dissolving dead skin at a different depth and speed. Knowing which one suits your skin type and concern determines whether you see clearer texture, fewer breakouts, or visible brightening, or end up with irritation and a compromised barrier. This guide maps where each acid works and how to pick yours.

What Chemical Exfoliants Do

Chemical exfoliants work by breaking the bonds between dead skin cells and the outer layer of skin, then washing away the debris. Unlike physical scrubs, which use friction, they dissolve on contact. The three main categories differ in molecular weight and water solubility, which controls how deep they penetrate and how fast they work.

AHA: The Surface Exfoliant for Dull and Dry Skin

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Alpha hydroxy acids are water-soluble and work only on the skin surface. Glycolic acid (from sugar cane) and lactic acid (from milk) are the most common. Glycolic acid has the smallest molecular weight of the AHAs, so it penetrates fastest and delivers quicker results, but carries higher irritation risk. Lactic acid is gentler and also hydrating, making it a better starting point for dry skin.

Popular AHA Products

The Ordinary Glycolic Acid 7% Toning Solution (around $6) offers strength at low cost. Paula’s Choice 8% AHA Gel (approximately $48) buffers the acid with a base and includes soothing ingredients. For stronger results, dermatology offices offer glycolic acid peels at 20% to 70% concentration.

What AHAs Treat

AHAs excel at smoothing rough texture, fading post-inflammatory hyperpigmentation (the dark marks left after acne heals), and brightening dull skin. They do not penetrate pores, so they do not directly unclog them. Results typically appear after two to four weeks of consistent use, two to three times per week. Start with 5% to 7% once or twice weekly, then increase frequency as your skin acclimates.

BHA: The Pore-Clearing Option for Oily and Acne-Prone Skin

Beta hydroxy acids are oil-soluble, meaning they slip inside pores and work below the skin surface. Salicylic acid is the only BHA approved by the FDA for over-the-counter use. Because it dissolves sebum, it is especially useful for congested, oily, and acne-prone skin.

Common BHA Products and Formats

Neutrogena 2% Salicylic Acid Acne Wash (around $5 to $8) offers an accessible cleanser formulation. Paula’s Choice 2% BHA Liquid Exfoliant (approximately $38) delivers salicylic acid in a hydrating base. CosRX BHA Blackhead Power Liquid (roughly $7 to $10) concentrates salicylic acid without humectants, targeting congestion with minimal additives.

How BHA Clears Congestion

BHAs reduce pore size temporarily by clearing them, shrink active breakouts, and prevent new comedones from forming. Most people notice improvement in congestion and breakout frequency after three to six weeks. Use two to three times per week initially, increasing to daily use only after establishing tolerance. A major caveat: salicylic acid is contraindicated in pregnancy. Consult your obstetrician before using it if you are pregnant or trying to conceive.

PHA: The Gentle Alternative for Sensitive and Compromised Barriers

Polyhydroxy acids are a newer category with a larger molecular weight than both AHAs and BHAs, so they stay on the surface longer and penetrate more slowly. Gluconolactone and galactose are the most common PHAs. This slower pace reduces irritation and inflammation.

Glossier Exfoliating Toner with Gluconolactone (around $29) layers easily and hydrates while exfoliating. Revision Skincare Gentle Exfoliating Powder with gluconolactone (approximately $55) works as a buffering exfoliant for reactive skin. Neutrogena Hydro Boost Hydrating Cleansing Wipes (roughly $4 to $6) include gluconolactone as a mild exfoliating agent in wipe form.

PHAs are ideal for sensitive skin, eczema-prone skin, and skin with a compromised barrier. They also offer humectant properties, meaning they help skin retain water. They do not deliver the fast brightening of glycolic acid or the pore-clearing power of salicylic acid, but they improve texture and tone without causing redness. Use daily, since their gentleness supports frequent application without irritation.

Choosing an Acid by Skin Type and Concern

Oily, Congested, and Acne-Prone

If your skin is oily with visible congestion and active breakouts, start with BHA at 1% to 2% salicylic acid, two to three times per week. If you prefer gentleness over speed, use gluconolactone PHA daily instead.

Dry and Sensitive

If your skin is dry or prone to sensitivity, begin with lactic acid AHA at 5% to 10%, twice per week, then graduate to glycolic acid only after confirming tolerance. For extremely reactive or compromised barriers, use PHA daily until the barrier heals, then introduce a stronger acid if needed.

Combination, Normal, and Hyperpigmentation

If you have combination skin (oily T-zone, dry cheeks), apply BHA only to congested areas and use AHA or PHA on dry zones. If hyperpigmentation or dullness is your primary concern and breakouts are not, AHA is the most direct route. If you have normal skin with no major concerns, any of the three works; start with an AHA or PHA to see which texture and tone benefits you notice first.

How to Layer and Apply Acids Safely

Never mix different acids in the same routine step. If you use a BHA cleanser in the morning, do not apply an AHA serum at night on the same day. Use one acid at a time, establish tolerance over several weeks, then consider introducing a second acid on different days of the week (BHA Monday, Wednesday, Friday; AHA Tuesday, Thursday, for example).

Apply acids to clean, completely dry skin—water dilutes them and reduces effectiveness. Wait five to ten minutes after cleansing before applying the acid. Follow with hydrating serum or moisturizer to buffer irritation. Never apply an acid immediately before going out in the sun; these exfoliants increase photosensitivity. Use broad-spectrum SPF 30 or higher every single day while using any exfoliant.

Do not combine acids with other potentially irritating ingredients such as retinoids, vitamin C, or benzoyl peroxide in the same routine, especially when starting. Once you have established tolerance to an acid, you can introduce other actives on separate days or at different times of day, but beginners should simplify.

When to Expect Results and Red Flags

Mild redness immediately after application is normal and fades within an hour. Persistent redness, burning, itching, or peeling that does not improve after one week signals over-exfoliation; reduce frequency to once per week or pause entirely. If redness worsens or a rash develops, stop the product and consult a dermatologist.

Visible improvements in texture and tone appear after two to four weeks of consistent use. Pore size reduction from BHA takes four to six weeks. If you see no improvement after six weeks, your skin may not respond well to that particular acid, the percentage may be too low for your needs, or the product formulation may not suit you—switch to a different acid category or a higher concentration.