Also known as: AHA, alpha hydroxy acid
What Is Glycolic Acid (AHA)?
Glycolic acid is an alpha hydroxy acid that can be derived from sugarcane, though most cosmetic glycolic acid is made synthetically. It has the smallest molecule of all the AHAs, which lets it penetrate the outer layer of skin quickly. There it loosens the bonds that hold dead cells together, so they shed more evenly instead of building up into a rough, dull layer.
The visible results are smoother texture, a more even surface that reflects light better and gradual fading of dark marks. With consistent use over months, glycolic acid may also help soften the look of fine lines and rough sun-damaged texture. How strong a product feels depends on both concentration and pH: a lower pH means more free acid and more exfoliation, but also more potential for irritation.
That small size is a double-edged sword. Glycolic acid tends to deliver faster results than larger AHAs such as lactic acid or PHAs, but it is also more likely to sting. AHAs also make skin more sensitive to the sun, which is why AHA products sold in the US often carry a sunburn alert on the label.
Glycolic Acid (AHA) Benefits for Skin
- Smooths rough, uneven texture.
- Helps brighten a dull, tired-looking complexion.
- Helps fade the look of post-blemish marks and sun spots over time.
- May soften the look of fine lines with long-term use.
- Helps other products spread and absorb more evenly.
How to Use Glycolic Acid (AHA)
Begin with a low-strength toner or serum two or three nights a week, applied to clean, dry skin. Follow with a moisturizer, and build frequency slowly as your skin adapts. Glycolic acid fits best in a night routine, away from retinoids — use them on different nights rather than together.
Sun protection is not optional with AHAs. Wear a broad-spectrum sunscreen every morning and reapply when you are outdoors for long periods (how to apply sunscreen). If you are unsure whether you need an AHA or a BHA, compare them in AHA vs BHA.
Side Effects & Precautions
Tingling on application is common, but burning, persistent redness, peeling or a raw feeling are signs to stop and let your skin recover. Overuse can weaken the barrier, leaving skin tight and reactive. Avoid applying it right after shaving, waxing or on sunburned skin.
People with very sensitive skin or deeper skin tones prone to dark marks after irritation should start especially gently, since irritation itself can trigger new pigmentation.
Use caution when combining
- Retinoids on the same night.
- Low-pH vitamin C serums applied in the same step.
- Freshly waxed, shaved or sunburned skin.
Frequently Asked Questions
How often should I use glycolic acid?
Most people do well with two to four times a week. Some tolerate daily use of a gentle toner, but more is not always better. Watch for tightness, stinging or flaking as signs to cut back.
Can glycolic acid be used on sensitive skin?
It is often too strong for very sensitive skin. Lactic acid or PHAs, which have larger molecules and penetrate more slowly, are usually more comfortable choices.
Why does glycolic acid make me more sensitive to the sun?
Removing dead surface cells leaves fresher skin that is less protected from UV. That is why daily sunscreen is essential while using AHAs and for a while after you stop.