Skin renews itself on its own, but not always at the same pace. As the years go by, with cold weather, with stress, or simply with a naturally thicker texture, surface cells tend to stay where they are for longer than they need to. You can see the result: a dull complexion, a less smooth texture, creams that seem to sit on the surface instead of sinking in. Alpha hydroxy acids exist to support that turnover, and the two most widely used in facial skincare — glycolic acid and mandelic acid — are not interchangeable at all.
What AHAs are
Alpha hydroxy acids (AHAs) are water-soluble organic acids: glycolic acid has historically been derived from sugar cane, mandelic acid from bitter almonds. They act on the outermost layer of the skin by weakening the bonds that hold spent cells in place, so that they detach gradually and evenly. It is a different mechanism from a scrub, which works through friction: here there is no abrasion at all, only a supported turnover.
In practice, the difference between the two acids comes down almost entirely to molecule size — and everything else follows from there.
Glycolic and mandelic: two different speeds
Glycolic acid
It is the smallest AHA molecule of all. It penetrates quickly and evenly, which is why it is the go-to active when skin is thick, tends towards oiliness, or looks dull or uneven in tone. That same speed that makes it effective, however, is also what makes it more demanding: on thin or reactive skin it can cause tingling, redness and a tight feeling. Faster does not mean more suitable.
Mandelic acid
Its molecule is considerably larger and crosses the stratum corneum more slowly. The exfoliation is more superficial and more gradual, with a generally better tolerability profile: it is the sensible choice for anyone with sensitive, dry or easily reddened skin, and for anyone approaching acids for the first time. Its affinity with lipid components also makes it interesting on combination skin with visible pores.
How to add them to your routine
AHAs are used in the evening, on clean, dry skin, before your cream. Start with two evenings a week and increase the frequency only if your skin responds well: brief tingling in the first few seconds is common, persistent burning with flaking is not.
In the days following application, exfoliation leaves skin more exposed to sunlight. Sun protection is non-negotiable: a high SPF every morning, reapplied during the day if you are outdoors. Also avoid layering AHAs and retinoids on the same evening, and pause for a few days if signs of irritation appear.
The Chrissie products we recommend
The AHA (Glycolic and Mandelic Acid) collection covers both routes, while the Exfoliants section brings together the full range of options.
- If your skin is reactive, or this is your first time — Mandelic Acid 30%, for gradual exfoliation that is well tolerated even on sensitive skin.
- If your skin texture is thick and your complexion dull — Glycolic Acid 10%, for more decisive renewal on skin already used to acids.
- If you have no idea where to start — begin with mandelic for a month and consider glycolic only afterwards, once you know your own tolerance threshold.
In short
- AHAs support the turnover of surface cells without any mechanical friction.
- Glycolic has the smaller molecule: it works quickly, but is more demanding on thin skin.
- Mandelic has the larger molecule: slower, more superficial, generally better tolerated.
- Use in the evening, starting twice a week and increasing only if your skin responds well.
- A high SPF every morning in the days following application.
- When in doubt, start with mandelic: you can always step up, whereas managing irritated skin is far more inconvenient.
