AHA vs BHA: chemical exfoliants explained
Glycolic, lactic, mandelic and salicylic acid compared, who each one suits and how to exfoliate without damaging your skin barrier.
Your skin sheds dead cells constantly, but sometimes they cling on, making skin look dull or rough and clogging pores. Chemical exfoliants loosen the bonds that hold those cells together so they release more evenly. Done right, the result is smoother, brighter skin. Done too often, the result is redness, stinging and a damaged barrier.
AHAs: alpha hydroxy acids
AHAs are water-soluble and work on the skin surface. They are a good fit for dullness, rough texture, uneven tone and mild sun damage.
- Glycolic acid: the smallest AHA molecule, so it penetrates easily. Effective but the most likely to sting. Originally associated with sugarcane.
- Lactic acid: larger and gentler, with some hydrating ability. A favorite for dry and sensitive skin. Associated with milk.
- Mandelic acid: larger still, slow and gentle. Often chosen for sensitive skin and deeper skin tones prone to dark marks. Derived from bitter almonds.
BHA: beta hydroxy acid
The BHA in skincare is salicylic acid. It is oil-soluble, so it can work inside oily pores, which makes it the go-to exfoliant for blackheads, clogged pores and acne-prone, oily skin. It is also mildly anti-inflammatory. In the US, over-the-counter acne products may contain salicylic acid at 0.5 to 2%.
PHAs: the gentle cousins
Polyhydroxy acids such as gluconolactone and lactobionic acid have large molecules that penetrate slowly. They exfoliate gently and attract moisture, so they are often tolerated by sensitive skin.
Which exfoliant fits you
| Your skin or goal | Try first | Typical frequency to start |
|---|---|---|
| Oily, blackheads, acne-prone | Salicylic acid (BHA) | 2 to 3 times a week |
| Dull, rough, sun-damaged | Glycolic or lactic acid (AHA) | 2 times a week |
| Dry | Lactic acid | 1 to 2 times a week |
| Sensitive | PHA or mandelic acid | 1 to 2 times a week |
| Combination | BHA on T-zone, lactic on cheeks | 2 times a week |
How to use exfoliating acids
- Use at night, after cleansing, on dry skin.
- Start with a low-strength leave-on toner or serum, a few nights a week.
- Follow with a moisturizer.
- Do not use on the same night as a retinoid while you are adjusting.
- Wear sunscreen daily. The US FDA advises sun protection while using AHAs and for a week afterward, because they increase sun sensitivity.
Signs of over-exfoliation include stinging when you apply plain moisturizer, a tight shiny look, flaking, new breakouts and redness. Stop all acids and retinoids for one to two weeks and focus on gentle cleansing and moisturizing.
Physical scrubs vs acids
Scrubs with gritty particles and brushes remove cells mechanically. Fine, round particles used gently are okay for some people, but jagged particles and hard scrubbing can cause tiny tears and irritation. Acids give more even results for most skin types.
At-home peels
Higher-strength peels (for example, 30% glycolic or higher) can be sold for home use, but they carry real risk of burns and dark marks, especially on deeper skin tones. Professional peels done by a trained clinician are safer for strong results.
General information only. Do not use acids on broken, sunburned or freshly waxed skin. See a dermatologist for persistent acne or pigmentation.
