Alpha hydroxy acids act on the surface. They loosen the bonds between corneocytes in the outermost layer of the skin, which produces a fast and genuinely visible change in smoothness and light reflection. That speed is their appeal and also their risk: the feedback is immediate, so people increase frequency, and the surface they are working on is finite.
The two worth knowing are glycolic acid, the smallest molecule and the most penetrating, and lactic acid, larger, gentler and humectant in its own right. For most men starting out, lactic acid is the better first choice.
Section 01Glycolic against lactic
| Glycolic acid | Lactic acid | |
|---|---|---|
| Molecule size | Smallest AHA | Larger |
| Penetration | Deeper | More superficial |
| Irritation potential | Higher | Lower |
| Additional property | None of note | Humectant, adds hydration |
| Typical home strength | 5 to 10 per cent | 5 to 10 per cent |
| Best starting choice | Experienced skin | Most people |
| Photosensitivity | Increased | Increased |
Both increase photosensitivity, which is not a marketing caution but a measurable effect. Sunscreen on the days after an acid night is part of the protocol, not an optional companion habit.
Section 02The protocol
Acid night
Total 02:50- 01
Cleanse and dry completely01:00
Wet skin changes the pH at the surface and dilutes the product unpredictably. Dry properly, which takes about a minute.
- 02
Apply thinly, avoiding the eye area and the corners of the nose00:20
A few drops or one pass with a soaked pad. There is no version of this where more product produces a better outcome.
- 03
Wait sixty seconds01:00
Stinging on application that fades within thirty to sixty seconds is expected. Burning that persists means rinse it off, and reduce the concentration next time.
- 04
Moisturise generously00:30
Non negotiable. A freshly exfoliated surface loses water faster, and this is the step that prevents the tightness people report the following morning.
- 05
Sunscreen the next morning, without exceptionNext AM
Photosensitivity is increased for several days after an AHA. This is the day the sunscreen is doing the most work.
Section 03Recognising over exfoliation
Over exfoliation does not look like irritation at first. It looks like good skin. The surface is smooth, light reflects evenly, and the effect is flattering under most lighting. Then it becomes shiny in a way that is not oil, tight through the day, and finally reactive to products that were previously fine.
Skin looks shiny but feels tight
That is a thinned surface, not hydration. Stop acids for two weeks and moisturise twice daily.
Moisturiser stings where it did not before
Stop all acids immediately and run the reset protocol. This is the definitive sign.
Fine lines look more visible after a period of frequent use
Dehydration at the surface makes lines more apparent. It reverses with recovery. Do not respond by exfoliating more.
Redness across the cheeks that lasts through the day
Stop. Two weeks minimum. If it has not settled, seek assessment rather than experimenting further.
You have been using an acid toner daily for months and it seems fine
It may be. Reduce to twice a week for a month and see whether anything gets better. Many people discover their baseline was worse than they thought.
Over exfoliation is the most common self inflicted skin problem in people who take skincare seriously. It is produced by exactly the behaviour that feels most conscientious: using the active more often because it seems to be working. If you are not sure whether you are over exfoliating, stop for two weeks. Nothing is lost and the answer becomes obvious.
Section 04Choosing a product
- A single acid at a stated concentrationFive to ten per cent for home use. Blends of three acids at unstated proportions cannot be assessed or ramped.
- A stated pH, or at least a stated leave on or rinse off intentAHA activity depends on pH. Products that state neither are asking you to guess at the effective dose.
- No physical exfoliant in the same productAcid plus grains is the fastest route to a compromised barrier available on a shop shelf.
- No fragrance if you are new to acidsThe sting from an acid is expected. The sting from fragrance on freshly exfoliated skin is avoidable.
- A format that controls quantityPre soaked pads deliver a large and inconsistent dose. A bottle you apply from is easier to keep at a fixed amount.
Section 05Who should use an AHA and who should not
| Situation | AHA | Better option |
|---|---|---|
| Rough texture, dull tone | Yes, lactic acid | Suitable as first choice |
| Blackheads and congestion | No | Salicylic acid, which is oil soluble |
| Inflammatory acne | No | Benzoyl peroxide or a retinoid |
| Post spot marks | Marginal | Azelaic acid or a retinoid |
| Rosacea or persistent redness | No | Azelaic acid, and a diagnosis first |
| Already using a retinoid four nights a week | One night only | Consider whether it adds anything |
| Currently reactive or in a reset | No | Bland care for fourteen days |
Section 06Body use, where AHAs are underrated
Alpha hydroxy acids are frequently more useful on the body than on the face. Lactic acid and urea preparations on the backs of the arms, the shins and the heels address rough keratinised skin that no facial routine touches. The area is larger, the skin is thicker, and the tolerance is correspondingly higher.
For rough bumps on the upper arms specifically, see the keratosis pilaris protocol, which is the one place in this publication where a daily acid is the recommended frequency rather than the warning.
The related documents are the salicylic acid protocol for oil soluble exfoliation, and the reset protocol for when this has gone too far.