Chemical exfoliation is the part of skincare most often used incorrectly. Used well, an acid can do quietly across weeks what a physical scrub never could. Used badly, the same acid produces tight, red, sensitised skin that takes a month to settle.
The first step in using them well is knowing the three families and the order of gentleness within each.
AHAs: alpha hydroxy acids
Water-soluble. They work on the surface of the skin, helping the upper layer of dead cells release. The result over weeks is smoother texture, brighter tone, and slightly faded surface pigmentation. The four most common, in order of gentleness:
Mandelic acid. The largest molecule of the AHA family, which is why it is the gentlest. Penetrates slowly, irritates rarely. A reasonable first AHA for sensitive or darker skin tones (lower risk of post-inflammatory pigmentation). Used at 5 to 10 percent in leave-on products.
Lactic acid. Mid-size molecule. Hydrating by nature, so feels softer on application than most acids. Used at 5 to 10 percent for surface renewal; higher percentages exist but are best avoided without acid experience.
Glycolic acid. The smallest, most-studied AHA. The strongest at equivalent percentages, the most likely to deliver dramatic-looking results, and the most likely to irritate. Used at 5 to 10 percent for leave-on at home; 20 to 70 percent in professional peels.
Citric acid. Often present in formulas as a pH adjuster rather than the active exfoliant. At higher concentrations it does exfoliate, but it is rarely the main acid in a leave-on product.
BHAs: beta hydroxy acids
Oil-soluble. The big difference. Because they are oil-soluble, they can penetrate sebum-filled pores, which AHAs cannot. This makes BHAs the right choice for congestion, blackheads, and most adult acne.
Salicylic acid. The standard BHA. Used at 0.5 to 2 percent in leave-on products, or 2 percent in cleansers (rinse-off). Anti-inflammatory in addition to exfoliating, which is why it suits acne-prone skin so well.
Betaine salicylate. A milder salicylic acid relative used in some Korean formulas. Often tolerated by skin that flushes on standard salicylic.
PHAs: poly hydroxy acids
The gentlest of the three families. Larger molecules, so they exfoliate the very surface without penetrating deeper, with much less risk of irritation. Often the right choice for sensitive skin, rosacea-prone skin, or anyone introducing acids for the first time.
Gluconolactone. The classic PHA. Mildly hydrating in addition to exfoliating. Used at 3 to 10 percent.
Lactobionic acid. Slightly stronger than gluconolactone. Antioxidant in addition to exfoliating. Used at 5 to 10 percent.
Which acid to pick
The question to ask first is not "which is strongest". It is "what does my skin actually need?".
- Dull tone, slight texture, sun-related pigmentation: AHA. Start with mandelic or lactic at 5 to 10 percent, twice a week, for the first month.
- Congestion, blackheads, adult breakouts: BHA. Salicylic acid at 1 to 2 percent, two to four evenings a week.
- Sensitive skin, rosacea-prone, never used acids: PHA. Gluconolactone at 5 to 10 percent, two to three evenings a week.
- Mixed concerns: often a single low-percentage AHA + BHA combination two evenings a week is more useful than alternating two single-acid products.
How to introduce one
Start at the lower end of the percentage range, twice a week, for two to three weeks. If skin is calm, build to three or four nights a week. Do not chase daily use; few skins benefit from daily acid exfoliation, and many become sensitised.
Apply to clean, dry skin in the evening. Follow with moisturiser. Skin under an acid is more sensitive to UV; daily SPF is non-negotiable.
The most common mistake is stacking acids with other actives on the same night. A vitamin C in the morning is fine. A retinoid on the same evening as a high-percentage AHA is not, for most skin. Alternate evenings instead.
When to stop
Persistent stinging on application, redness that does not settle within minutes, tight skin that lingers across days, a sense of thinness or shine that did not exist before: any of these is a signal to step back. Reduce frequency, lower percentage, or pause for two weeks and reintroduce more slowly. Acids do not punish a pause.
The gentlest acid that addresses your concern is almost always the right answer. The strongest acid you can tolerate is the wrong question.
Key takeaways
- AHAs work on the surface; BHAs work in pores; PHAs are the gentlest of the three.
- Mandelic is the gentlest AHA, glycolic the strongest. Salicylic is the standard BHA.
- Sensitive or first-time skin starts with a PHA; congestion-prone skin starts with a BHA.
- Two to three evenings a week is a reasonable cadence; daily acid use rarely helps.
- Daily broad-spectrum SPF is essential while using any chemical exfoliant.
Common questions
Can I use an AHA and a BHA at the same time?
Yes, in a combined formula, and many work that way. Stacking two separate products is harder for skin to handle; alternate nights is usually wiser.
How long until I see results?
Surface texture and brightness in two to three weeks. Tone evenness in six to eight. Pigmentation in twelve weeks or longer. The arc is steady, not dramatic.
Is glycolic acid bad for darker skin tones?
Not bad, but worth using carefully. Aggressive exfoliation on melanin-rich skin can trigger post-inflammatory hyperpigmentation. Mandelic acid is often a more forgiving first choice.
Should I use an acid toner daily?
Few skins benefit from a daily leave-on acid. Most do better with two to four evenings a week. The product marketing pushes daily use; the dermatology consensus is more conservative.
Cura is informational and not a substitute for medical advice. Severe or persistent acne, rosacea, and pigmentation conditions benefit from dermatologist assessment alongside over-the-counter products.