Skin · actives
Exfoliation: AHA, BHA and how often is enough
Chemical exfoliants can smooth texture and clear pores. Used too often, they cause exactly the problems people buy them to fix.
What exfoliation does
The outer layer of skin sheds constantly, but not always evenly. Exfoliation loosens the bonds between dead cells so they come away sooner, which can make the surface look smoother and more even and help keep pores clear. Chemical exfoliants do this with acids; scrubs do it with friction, which is harder to control.
AHA: for the surface
Alpha-hydroxy acids such as glycolic and lactic acid are water-soluble and work mainly on the surface. In a small clinical study, an AHA lotion used on sun-damaged skin for six months thickened the skin and improved signs of sun damage seen under the microscope. Lactic acid is generally gentler than glycolic acid and suits drier or more sensitive skin.
BHA: for pores
Salicylic acid, the common beta-hydroxy acid, is oil-soluble, so it can work inside the pore as well as on the surface. That makes it the better fit for blackheads, oily skin and acne-prone skin. Reviews of salicylic acid also describe an anti-inflammatory effect, which is part of why it is used in acne care.
How often
Two or three evenings a week is a sensible start for a leave-on acid; some people tolerate more, many don't need more. Don't introduce an acid and a retinoid at the same time, and don't use them on the same night until you know how your skin reacts. More frequent or stronger is not better: the right dose is the lowest one that does the job.
Sun sensitivity
Acids that remove the outermost layer of skin can make it more sensitive to the sun, especially alpha-hydroxy acids. Use broad-spectrum sunscreen every morning while you exfoliate, and for a while after you stop.
Signs you're overdoing it
Stinging when you apply a plain moisturizer, tightness, a shiny or waxy look, new redness or flaking, and breakouts that started with the new product are classic signs of over-exfoliation. Stop all acids and scrubs for one to two weeks and keep to a gentle cleanser, moisturizer and sunscreen until the skin settles. Stronger in-clinic peels exist, but they are a different tool and belong with a trained professional.
Sources
- Effects of alpha-hydroxy acids on photoaged skin: a pilot clinical, histologic, and ultrastructural study — Journal of the American Academy of Dermatology (1996)(Opens in a new window)
- Salicylic acid as a peeling agent: a comprehensive review — Clinical, Cosmetic and Investigational Dermatology (2015)(Opens in a new window)
- Chemical peels in aesthetic dermatology: an update 2009 — Journal of the European Academy of Dermatology and Venereology (2010)(Opens in a new window)
