iStylish Chemical Exfoliation Guide: AHAs, BHAs, and PHAs Explained
Chemical Exfoliation Guide: AHAs, BHAs, and PHAs Explained
Chemical exfoliation replaces the brute force of physical scrubs with molecular precision. Alpha hydroxy acids, beta hydroxy acids, and polyhydroxy acids each target different skin concerns through different mechanisms, and understanding which acid does what prevents the trial-and-error frustration that sends many people back to their washcloths.
How Chemical Exfoliation Works
Your skin sheds roughly forty thousand dead cells every hour, but that shedding process slows with age, sun damage, and dehydration. When dead cells accumulate on the surface, skin looks dull, feels rough, and pores become congested. Chemical exfoliants dissolve the bonds holding those dead cells together, allowing them to release naturally without the micro-tears that physical scrubs can cause.
The pH of a chemical exfoliant determines its effectiveness. Most acids work best between pH 3.0 and 4.0. Products formulated above pH 4.5 may feel gentler but deliver significantly less exfoliation. This is why the same percentage of glycolic acid can feel dramatically different across two products — the pH makes the difference.
Alpha Hydroxy Acids
AHAs are water-soluble acids derived from natural sources. They work on the skin’s surface, making them ideal for addressing dullness, fine lines, uneven texture, and sun damage.
Glycolic acid is the smallest AHA molecule, which means it penetrates most effectively. Concentrations between five and ten percent are suitable for home use. It is the most researched AHA and has proven benefits for collagen stimulation and hyperpigmentation.
Lactic acid is larger and gentler than glycolic acid. It also functions as a humectant, drawing moisture into the skin while exfoliating. Concentrations of five to ten percent work well for sensitive or dry skin types that find glycolic acid too intense.
Mandelic acid has the largest AHA molecule, making it the gentlest option. It is particularly effective for acne-prone and darker skin tones because its slow penetration reduces the risk of post-inflammatory hyperpigmentation.
Beta Hydroxy Acids
BHA refers almost exclusively to salicylic acid in skincare. Unlike AHAs, salicylic acid is oil-soluble, which means it can penetrate into pores and dissolve the mix of sebum and dead cells that causes blackheads, whiteheads, and acne.
Salicylic acid at two percent concentration is the standard for home use. It also has anti-inflammatory properties, which is why it calms existing breakouts rather than just preventing new ones. People with oily or acne-prone skin benefit most from BHA, though it can be drying if overused.
A key advantage of BHA is that it causes less sun sensitivity than AHAs. While sunscreen is still essential during any exfoliation regimen, BHA users have a slightly wider margin of safety with incidental sun exposure.
Polyhydroxy Acids
PHAs are the newest generation of chemical exfoliants. Gluconolactone and lactobionic acid are the most common. Their molecules are significantly larger than AHAs, which means they work exclusively on the outermost layer of skin and cause minimal irritation.
PHAs also function as humectants and antioxidants, providing hydration and environmental protection alongside exfoliation. They are suitable for people with rosacea, eczema, or extremely sensitive skin who cannot tolerate traditional acids.
The trade-off is potency. PHAs produce gentler results than AHAs or BHAs, so they are better for maintenance than for correcting significant texture or pigmentation issues.
How to Choose the Right Acid
| Skin Concern | Best Acid | Recommended Concentration |
|---|---|---|
| Dullness and fine lines | Glycolic acid (AHA) | 5-10% |
| Dry, sensitive skin | Lactic acid (AHA) | 5-10% |
| Acne-prone, dark skin tones | Mandelic acid (AHA) | 5-10% |
| Oily skin and clogged pores | Salicylic acid (BHA) | 1-2% |
| Rosacea or very sensitive skin | Gluconolactone (PHA) | 5-15% |
How to Introduce Chemical Exfoliants
Start with one acid, used once or twice per week, at the lowest effective concentration. Apply it after cleansing on dry skin and wait two to three minutes before applying the next step in your routine. Monitor your skin for signs of irritation such as persistent redness, peeling, or stinging that lasts beyond the initial application.
After two to three weeks without irritation, increase frequency gradually. Most skin types tolerate chemical exfoliation three to four times per week once acclimated. Daily use is possible with gentler acids like PHAs or low-concentration lactic acid, but aggressive daily use of glycolic or salicylic acid risks barrier damage.
Never combine multiple acids in the same routine unless a product is specifically formulated with a blend. Layering glycolic acid under salicylic acid, for example, dramatically increases irritation risk without proportional benefit.
Sunscreen Is Non-Negotiable
AHAs increase photosensitivity by roughly two to four times during use. This makes daily broad-spectrum SPF 30 or higher absolutely essential. Even on cloudy days and even if you work indoors, UV exposure through windows can cause hyperpigmentation on freshly exfoliated skin. Skipping sunscreen while using chemical exfoliants can worsen the very concerns you are trying to address.
When to See a Professional
If over-the-counter concentrations are not producing results after eight to twelve weeks of consistent use, a dermatologist can offer professional-strength peels with concentrations of twenty to seventy percent. These clinical treatments produce dramatic results but require professional application and specific aftercare protocols.
For a deeper look at how exfoliation fits into a complete routine, see our Skincare Routine for Oily Skin. If you want to protect your barrier while using active ingredients, our Skin Barrier Repair Guide covers recovery strategies.