These are exfoliating toners containing alpha-, beta- or poly-hydroxy acids such as glycolic, lactic, or malic acids (AHAs), salicylic acid (BHA), or gluconolactone and lactobionic acids (PHAs).

Glycolic acid toner brightens and freshens the complexion by chemically exfoliating the top layer of dead skin cells, revealing the fresher skin underneath. It does this by denaturing (i.e. interfering with) the protein bonds that hold these dead skin cells onto the surface of the skin, where they don’t really do anything but dull and roughen the skin. Breaking these bonds allows the dead cells to be wiped off of the surface.

Like all the hydroxy acids, glycolic acid helps to improve hydration within the skin and will help to soften irregular pigmentation, too. A glycolic acid toner can help calm down acne by unblocking the pores on the surface of the skin, but it can’t reach into blocked pores in the way that a salicylic acid toner can.

I’d start off by using it twice a week at first, and seeing how your skin responds. If your skin is fine with it, then step your usage up to every other day. Lots of people seem to like to use glycolic toners every day, but I would not advise this – multiple skincare experts have advised me that we tend to overuse alpha hydroxy acids, which can end up damaging the skin barrier and leading to pigmentation issues.

Don’t use glycolic acid toner if you’re also using a glycolic acid face wash, as this is likely to be too much for your skin to handle.

If the glycolic acid is irritating your skin – i.e. leaving it peeling, red and sore – then step down your usage. Always respond to how your skin is reacting to a product, and don’t think that you should ‘push through’ any redness or irritation. Redness signals inflammation, which is bad for the skin, so if your skin is unhappy, back off and go more slowly.

Wet a cotton pad with some of the toner, and wipe it over a clean, dry face (i.e. use this toner after cleansing, so that the toner doesn’t have to fight its way through grime and oil on the surface of your skin in order to do its job).

After using a glycolic acid toner you can apply a treatment serum if you are using one, and/or a moisturiser. In the morning, make sure you always finish your skincare regime with a sunscreen. You should be wearing sunscreen every day as a matter of course, but it is particularly important if you are using a glycolic acid toner as this will make your skin more sensitive to ultra violet light.

Not at the same time. Use them on alternate nights. Using them simultaneously would really run the risk of irritating your skin, so you definitely need to be cautious and avoid using them at the same time. I would use the toner a couple of times a week in the morning, and then use the retinol at night. Also, depending on the formulation of the product, retinol may counteract the effects of the glycolic acid.

Added to this, you need to know that if you’re using an alpha hydroxy acid lotion in the evening, you’ll get stronger results if you don’t put anything on afterwards. Any product with water in it – e.g. serum or moisturiser – will neutralise the acid, so it’s stronger if you leave it on its own. If you’re wondering what that means for the acid toner you were planning to use before your serum and sunscreen – it’s fine, but you’ll get more of an exfoliating, brightening result if you used the acid product on its own in the evening.

Yes you can – a lot of people will use an acid toner in the morning and then put a vitamin C straight on afterwards. If your skin doesn’t like this combination, however, just don’t do it.

No – hyaluronic acid is a different type of acid to the AHAs, BHA and PHAs. It’s hydrating, rather than exfoliating, so hyaluronic acid is usually an ingredient in moisturisers, hydrating serums and hydrating face masks rather than in toners. You could, however, find hydrating toners that do contain hyaluronic acid – but as an ingredient, it’s not a toner in itself.

BHA stands for beta hydroxy acid. There is only one beta hydroxy acid, and that is salicylic acid. Like alpha hydroxy acids (AHAs), BHA has an exfoliating effect on the skin by dissolving the ‘cellular glue’ that is holding old, dead skin cells onto the skin surface, so using this kind of toner will give you fresher, smoother skin. Also, just like AHAs, BHA will help your skin to improve its hydration levels.

BHA is also a really useful ingredient in skincare because it is oil-soluble. This means it can work its way into pores that have become clogged with oil, and help clear them out from the inside. Keeping pores clear like this reduces the chances of spots and breakouts. Another benefit of BHA toner is that it is anti-inflammatory, so it can bring down redness and inflammation in spotty skin.

Yes, a BHA/ salicylic acid toner is really helpful in managing spotty or congested skin, because it will help keep pores clear, give the skin surface a gentle exfoliation, reduce inflammation and improve moisture levels within the skin.

Lactic acid is an alpha hydroxy acid (AHA), like glycolic acid. It is a larger-sized molecule than glycolic acid, so it doesn’t penetrate the skin so quickly as glycolic acid. You will often find acid toners which combine lactic and glycolic acids because lactic acid is more gentle on the skin than glycolic acid.

That depends on what you want it to do.

f you have congested or spotty skin, choose a BHA/ salicylic acid toner.

If you are looking for a skin-brightening, radiance-boosting effect, choose an AHA toner with glycolic and/or lactic acid.

If you have sensitive skin, look for a toner with a poly hydroxy acid (PHA) such as gluconolactone or lactobionic acid, as this will give your skin similar effects, but more slowly, at a concentration that your skin will find easier to tolerate.