AHA: morning or evening?

Evening. AHAs are exfoliating acids that increase skin's sun sensitivity for several days—applying them in the morning necessitates flawless sun protection, which few routines maintain. But timing is only the first of the common mistakes with these acids. Here are six, in order of how much damage they cause.

Mistake 1 — using them in the morning without sunscreen

This mistake negates everything else. A glycolic acid applied in the morning to skin that will go out without protection causes more spots than it erases.

Induced photosensitivity lasts for several days after application, not just on the day of. Daily sun protection is therefore necessary even when applying the acid in the evening.

Applying in the evening solves half the problem: the skin is not exposed in the hours that follow, when it is most vulnerable.

Mistake 2 — confusing AHA and BHA

AHAs — glycolic acid, lactic acid, mandelic acid — are water-soluble and work on the surface. BHA, or salicylic acid, is oil-soluble and penetrates the pore.

This difference dictates the choice. A dull complexion, fine lines, uneven texture call for an AHA. Blackheads and oily skin call for a BHA.

Using both on the same evening provides nothing more than irritation. Alternate if you have both needs.

Mistake 3 — starting too strong

A concentration of 5 to 8% is sufficient to start, two evenings a week. Products at 10% or 15% exist and work, but they are not a starting point.

Mandelic acid is the mildest of the AHAs — its molecule is larger, so it penetrates more slowly. It is the right choice for sensitive skin that wants to try.

Glycolic acid is the most powerful and most studied. It is also the most irritating, and requires a gradual increase over two months.

Mistake 4 — believing it needs to sting

A slight tingling for a few seconds is normal. Burning, lasting redness, or peeling skin in patches are not.

Effective exfoliation is not visible exfoliation. A well-executed routine with AHAs results in a brighter complexion without anything visibly flaking off.

If your skin is peeling, you're doing too much. Space out applications, and resume when comfort has returned.

Mistake 5 — forgetting to moisturize afterwards

An exfoliating acid removes; you must replenish. A cream afterwards is not optional; it's what makes the routine sustainable in the long run.

Hyaluronic acid goes in between: after the acid, before the cream, on slightly damp skin. This combination almost entirely compensates for the hydration lost through exfoliation.

A light texture in the evening is sufficient for oily skin; a rich cream is better suited for dry skin. Skin type determines the texture, not the principle.

A gentle cleanser also matters. Using a harsh foaming gel followed by an acid is like combining two aggressions.

The serum plays a precise role here. A hyaluronic acid serum applied immediately after the acid replenishes the hydration lost by exfoliation, and prepares the skin for the cream that follows.

The complementary care products for an AHA are as important as the acid itself. A gentle cleanser, a hydrating serum, a cream: these three products make the difference between a routine you stick with for six months and one you abandon in three weeks.

The glow we seek comes from there, by the way. Exfoliated but dehydrated skin appears dull; it is hydration that provides the glow, exfoliation merely clears the way.

Mistake 6 — layering them with retinol

Never on the same night. Retinol and AHAs stress the skin in two different ways that add up, and the result is a damaged barrier.

Alternate: acid one night, retinol the next, and a night off in between if your skin is reactive. This organization requires a bit of discipline and avoids a lot of trouble.

Vitamin C should be kept for the morning. This is not a chemical incompatibility, but a matter of burden on the same skincare routine.

When morning use is defensible

A glycolic acid cleanser, rinsed off immediately, poses less of a problem. The contact time is short and the amount of acid remaining on the skin is low.

A low-concentration lotion, under an SPF 50 sunscreen applied correctly and reapplied, is still possible. It's demanding, and you have to be honest about what you actually do.

When in doubt, use in the evening. It's simpler to maintain, and simplicity is what makes a routine last.

According to your skin type

Oily skin: glycolic acid, every other night eventually. It tolerates it well and benefits greatly.

Dry skin: lactic acid, which is also a humectant. Twice a week, with a rich cream afterwards.

Sensitive skin: mandelic acid, once a week to start. Many sensitive skins can use an AHA — provided they choose the right one and go slowly.

Mature skin: glycolic acid remains the most well-documented for complexion and texture. Allow three months of regular use before judging.

The choice of serum follows the skin type. A fluid texture for oily skin, a richer serum for dry skin, and in all cases a cream on top.

The active ingredients to avoid in parallel are the same for everyone: no retinol on the same night, no second acid, no mechanical exfoliation in the same week.

Using a soap-free cleanser remains the rule, regardless of skin type. It is the most neglected product and the one that causes the most damage when poorly chosen.

What AHAs don't do

They do not treat inflammatory acne. For deep lesions, dermatological advice is necessary.

They do not erase spots in a few weeks. Improvement takes months and is undone by the first summer without protection.

They do not replace a moisturizer or sunscreen. An acid without these two companions does more harm than good.

The fifth mistake is the most common

Forgetting to moisturize after the acid negates part of the benefit and creates the discomfort that makes people stop altogether. A 10% lactic acid AHA peel that already contains a humectant reduces this risk, without negating the need for cream the next day.