Chemical Exfoliants Explained: AHA vs BHA vs PHA

Chemical exfoliants are some of the most transformative products you can add to your routine — and some of the easiest to misuse. AHAs, BHAs, and PHAs each dissolve dead skin cells and promote renewal, but they work differently, target different concerns, and suit different skin types. Choosing the wrong one, or using it too often, can wreck your skin barrier in days.

This guide breaks down each type, explains how to use them safely, and helps you pick the right exfoliant for your skin.

What Is Chemical Exfoliation?

Chemical exfoliation uses acids or enzymes to dissolve the bonds holding dead skin cells to the surface. Unlike physical exfoliation (scrubs, brushes, washcloths), chemical exfoliants work evenly across the skin without requiring any rubbing or pressure. This makes them gentler in some ways and more consistent in their results.

The three main categories of chemical exfoliants are:

• AHAs (Alpha Hydroxy Acids) — Water-soluble acids that work on the skin surface
• BHAs (Beta Hydroxy Acids) — Oil-soluble acids that penetrate into pores
• PHAs (Polyhydroxy Acids) — Larger-molecule acids that exfoliate with minimal irritation

Each has distinct strengths, and understanding those differences is the key to choosing correctly.

AHAs: Alpha Hydroxy Acids

What They Are

AHAs are water-soluble acids derived from natural sources — sugarcane, milk, fruits, and almonds. They work on the skin's surface by dissolving the "glue" (desmosomes) that holds dead cells together, revealing fresher skin underneath.

Common AHAs

• Glycolic acid — The smallest molecule, deepest penetration, most potent. Derived from sugarcane. Best for experienced users.
• Lactic acid — Slightly larger molecule, gentler than glycolic. Also provides mild hydration. Good entry point for beginners.
• Mandelic acid — Even larger molecule, very gentle. Effective for darker skin tones that are prone to post-inflammatory hyperpigmentation.
• Tartaric acid — Derived from grapes, typically used in combination with other AHAs.
• Citric acid — Primarily used as a pH adjuster, mild exfoliant at higher concentrations.

Best For

• Dull, rough skin texture
• Sun damage and photoaging
• Hyperpigmentation and uneven tone
• Fine lines and surface wrinkles
• Dry skin (especially lactic acid, which has humectant properties)

How to Use

AHAs are typically used 2 to 3 times per week. Apply them after cleansing and toning, on dry skin. Wait 15 to 20 minutes before applying your next product to allow the acid to work at its optimal pH.

Start with lower concentrations:

• Glycolic acid: Start at 5-8%, work up to 10-15%
• Lactic acid: Start at 5%, work up to 10%
• Mandelic acid: Start at 5-10%, work up to 15%

Important Warning

AHAs increase photosensitivity significantly. If you use AHAs at night, you must wear sunscreen the next morning — and every morning. Skipping sunscreen while using AHAs will cause more sun damage than if you had not exfoliated at all.

BHAs: Beta Hydroxy Acids

What They Are

BHAs are oil-soluble acids, which means they can penetrate through the oil that lines your pores. This ability to work inside pores is what makes BHAs uniquely effective for acne and congestion.

The Main BHA

Salicylic acid is the primary BHA used in skincare. While technically there are other BHAs, salicylic acid dominates the category so thoroughly that "BHA" and "salicylic acid" are used almost interchangeably.

Salicylic acid is derived from willow bark and is related to aspirin, which explains its anti-inflammatory properties.

Best For

• Acne and breakouts (all types)
• Blackheads and whiteheads
• Enlarged or congested pores
• Oily skin
• Sebaceous filaments on the nose
• Milia (small white bumps)

How to Use

BHAs can be used 2 to 3 times per week for treatment, or daily at lower concentrations (0.5-1%) for maintenance. Apply after cleansing, on dry skin. Wait 15 to 20 minutes before the next step.

Common concentrations:

• Daily use: 0.5-1% salicylic acid
• Treatment use: 2% salicylic acid (the maximum for over-the-counter products in most countries)
• Professional peels: 20-30% (only performed by dermatologists or trained estheticians)

BHA Advantage Over AHA for Acne

AHAs only work on the surface. They cannot get inside a clogged pore. BHA can. This is why salicylic acid clears blackheads and prevents new breakouts — it dissolves the sebum and dead cells inside the pore, not just the ones on top.

PHAs: Polyhydroxy Acids

What They Are

PHAs are the newest generation of chemical exfoliants. They have larger molecular structures than AHAs, which means they cannot penetrate as deeply. This sounds like a disadvantage, but it is actually their greatest strength: they exfoliate the surface without causing the irritation and sensitivity that AHAs can trigger.

Common PHAs

• Gluconolactone — The most widely used PHA, provides gentle exfoliation plus humectant benefits
• Galactose — Mild exfoliant with moisture-binding properties
• Lactobionic acid — Antioxidant properties in addition to exfoliation

Best For

• Sensitive skin that cannot tolerate AHAs or BHAs
• Rosacea-prone skin
• Eczema (when exfoliation is needed but traditional acids cause flare-ups)
• Beginners who have never used chemical exfoliants
• Skin currently using retinol (PHAs are least likely to cause over-exfoliation when combined)

How to Use

PHAs can be used daily for most skin types, or every other day for very sensitive skin. Wait times are shorter — 5 to 10 minutes is usually sufficient before the next step.

PHA Advantages

• Do not increase sun sensitivity as much as AHAs
• Provide humectant benefits (they attract water to the skin while exfoliating)
• Anti-glycation properties (gluconolactone specifically helps prevent collagen stiffening)
• Gentle enough to use alongside retinol

How to Layer Chemical Exfoliants

Chemical exfoliants are pH-dependent — they need an acidic environment to work. This affects when you apply them and how long you wait between steps.

The Correct Routine Placement

1. Cleanser — pat skin dry
2. Chemical exfoliant — apply to dry skin
3. Wait 15 to 20 minutes (AHA/BHA) or 5 to 10 minutes (PHA)
4. Toner (optional, hydrating only — not another exfoliating toner)
5. Serum
6. Moisturizer
7. Sunscreen (AM)

Apply exfoliants to dry skin, not damp. Water dilutes the acid and raises the pH, reducing effectiveness. The wait time allows the acid to work at its intended pH before you layer products that may neutralize it.

For the complete product order with all steps mapped out, the skincare layering order guide is your reference.

Which Night: Exfoliant or Retinol?

Do not use chemical exfoliants and retinol on the same night, especially when you are starting out. Both increase cell turnover, and combining them can destroy your barrier. Instead, alternate:

• Monday, Wednesday, Friday: Chemical exfoliant
• Tuesday, Thursday, Saturday: Retinol
• Sunday: Neither (recovery night)

Once your skin is fully adjusted to both (after 2 to 3 months), some people can tolerate gentle exfoliants and retinol on the same night. But this is the exception, not the rule.

How Often to Exfoliate

Over-exfoliation is the most common mistake in skincare. Your skin does not need daily exfoliation with strong acids. Here are general guidelines:

Start at the lower end and increase gradually. If your skin starts feeling tight, stinging with products that did not sting before, or looking shiny and raw, you are overdoing it. Scale back immediately.

Common Mistakes to Avoid

Using Multiple Exfoliants at Once

An AHA toner followed by a BHA serum followed by a PHA moisturizer is a recipe for a destroyed barrier. Pick one type of chemical exfoliant per routine session. You can alternate types on different days if your skin tolerates it.

Exfoliating in the Morning Without Sunscreen

If you exfoliate in the morning (which is fine with PHAs or low-concentration BHAs), sunscreen is mandatory. AHAs in the morning are risky because of photosensitivity — night use is safer for glycolic and lactic acid.

Applying to Damp Skin

Water on the skin dilutes chemical exfoliants and changes their pH. Always apply to dry, clean skin for optimal results.

Not Moisturizing After

Chemical exfoliation removes the outermost layer of dead cells, which means your barrier is temporarily thinner. Follow up with a solid moisturizer to protect the newly revealed skin. Ceramide-rich moisturizers are especially good after exfoliation.

Combining With Physical Exfoliants

Using a chemical exfoliant and then scrubbing with a washcloth or brush is asking for irritation. Pick one method per routine. If you use a chemical exfoliant, skip physical exfoliation entirely that day.

Ignoring Your Skin's Signals

Tingling is normal. Burning, stinging, or visible redness that lasts more than a few minutes is not. If an exfoliant hurts, wash it off and reassess. You may need a lower concentration, a gentler type (switch from glycolic to mandelic, or from AHA to PHA), or less frequent use.

Building an Exfoliation Schedule

When your routine involves different actives on different nights — exfoliant Monday, retinol Tuesday, treatment serum Wednesday — keeping track of what goes where is a real challenge. Layered lets you create separate routines for exfoliant nights and retinol nights, each with the right wait times for that session, so you never mix things up.

Quick Decision Guide

Choose AHA if: You want smoother texture, brighter skin, and reduced surface pigmentation, and your skin can handle some adjustment.

Choose BHA if: Acne, blackheads, or clogged pores are your main concern, and you have oily or combination skin.

Choose PHA if: You have sensitive skin, rosacea, or have not tolerated other acids in the past, but still want the benefits of exfoliation.

Use a combination (on different nights): If you have multiple concerns — like acne plus dullness — alternate BHA and AHA on separate nights.

The Bottom Line

Chemical exfoliation is one of the highest-impact changes you can make to your skincare routine, but it demands respect. Start with the gentlest option for your skin type, use it infrequently until you know how your skin responds, and always pair it with moisturizer and sunscreen.

More exfoliation is not better. Better exfoliation — the right type, the right frequency, the right technique — is better. Find your sweet spot, protect your barrier, and let the acids do their work.