05 ACID SERUM OR ACID TONER?

What’s the difference? While acid toners and serums may often contain the same active ingredients, they’re based in different vehicles, and used in quite different ways. The difference lies in the formulation, explains Dr Shotter. ‘An acid toner will be waterbased, and it may sting more because of the rapid penetration into the skin. A serum, on the other hand, will release the acid more slowly and combines it with humectants, which will not just exfoliate the dead surface layer of the skin but also nourish and hydrate the underlying skin cells, so it’s more beneficial.’ Different acids can benefit different skin types. Alpha hydroxy acids (AHAS), such as glycolic, lactic and azelaic, are good for dullness, or early signs of ageing; studies show they help to initiate collagen synthesis in the skin, so are able to minimise the appearance of fine lines and wrinkles. A beta hydroxy acid (BHA), such as salicylic acid, is great for blemish-prone skin – unlike AHAS, it’s able to cut through oil, allowing it to unclog pores and blitz away dead skin cells and dirt. It also has antibacterial properties – happily, stopping spots from forming. ‘Acid serums tend to be the most beneficial in the long term as the ingredients are more concentrated and penetrate the skin at a deeper level to work more effectively,’ adds Dr Wedgewood, while acknowledging that a toner may be a good starting point if you already have a number of steps in your regime, or your skin is a little more sensitive.

How to use them: Toners are made to be used with a cotton pad and swept across the skin, while serums are massaged in and left on. AHA toners and serums are generally applied during your evening skincare routine, as this is when your skin cells are kicked into repair mode. (They don’t call it beauty sleep for nothing.) BHA toners can be applied both morning and night to help tackle acne.

WH picks: Sunday Riley Good Genes Glycolic Acid Treatment, £85; Pixi Clarity Tonic, £10; The Inkey List Lactic Acid, £7.99