Whilst we know the word acid can sometimes seem a little daunting when it comes to skincare, they're actually really great for skin and can combat everything from texture, tone to hydration. From salicylic to glycolic and lactic, are being incorporated into the skincare routines of most people who are serious about skincare.

One of the most proven ingredients to reduce breakouts, unclog pores, and improve hydration and skin tone is salicylic acid (BHA). BHA is an exceptionally gentle exfoliant that helps skin cells to shed as they did when we were young. As we age, mostly due to sun damage or if you tend to breakout, skin can’t exfoliate naturally on its own. That’s where BHA steps in to help skin behave young again.

The clear concoctions are exfoliators extraordinaire – capable of burying into your pores to dissolve build ups of oils and sebum which, as you know, are what cause blackheads and blemishes.

To get the detail, TTBC chatted to Jennifer Rock, creator of The Skin Nerd online skin consultancy and the author of The Skin Nerd: Your straight-talking guide to feeding, protecting and respecting your skin (£17.99, Headline). Here's her answers to your top acid questions.

From Salicylic To Lactic Acid: Your 101

Why Have Acids Become Such A Thing In The Skincare World?

With the ban of micro-beads in Europe, it has given exfoliation with acids a spot on the stage. Personally I’ve always fought for the use of chemical exfoliation over mechanical exfoliation (such as scrubs, grits and brushes) as mechanical exfoliation can cause little tears on the surface of your skin.

Acids are very trendy, but the word can make people panic. In reality, our skin’s pH is naturally and ideally acidic, so acids work with that.

Why Are Acids Effective, When It Comes To Skincare?

Exfoliating acids, such as lactic acid, polyhydroxy acids, glycolic acid, mandelic acid and salicylic acid, dissolve the desmosomes, our skin cells’ 'binding agent' that holds dead skin cells to each other.

At the same time, they encourage skin cell turnover to speed up, essentially prompting the skin’s own exfoliation process.

Before Using Acids What Should Everyone Know?

What I see a lot of with my clients is over-exfoliation, due to a lack of education surrounding these powerful ingredients.

Brands like [cult cheap skincare brand] The Ordinary retail potent acid solutions with light information or guidance, so consumers can end up putting concoctions of salicylic acid, lactic acid and retinol on their face every night, for example. This is too much, and can damage your skin’s barrier.

You need patience and care when it comes to using acids. Start out using them once every two or three days, or even once a week. When you know how your skin will behave, you can start to very slowly up your usage.

When you’re using exfoliating acids, the rest of your routine should be hydrating, nourishing and skin-barrier-friendly too. Vitamins, hyaluronic acid and ceramides will help to ensure that your skin is not overwhelmed by the acid exfoliation.

How Should We Be Using Acids?

Skin experts, facialists and dermatologists all have their own ideas about how people should be exfoliating. I believe that the best mode is to use an exfoliating cleanser at night once every two or three days, depending on whether your skin is resilient or a touch reactive.

What’s The Best Acid For Different Skin Types?

AHAs, or alpha-hydroxy acids, are water-soluble, whereas BHAs, or beta-hydroxy acids, are oil-soluble.

• AHAs are usually recommended for those who would be more prone to dryness, dehydration and pigmentation

• BHAs are fabulous for those who would get spots, blackheads, acne and oiliness

How To Use Salicylic acid

Salicylic acid is a BHA which simultaneously prompts the skin to exfoliate itself whilst burrowing into the pore and dissolving sebum and debris. From this description, you may be able to guess that it is the ideal acid for those with oily or acne-prone skin. The general rule to apply this type of leave-on exfoliant after cleansing and toning. You would then follow with the rest of your skincare routine. During the day, the last product you apply should always be sunscreen.

Salicylic acid is mostly recommended for those with combination to oily or acne-prone skin. It can also be very helpful for rosacea and reducing redness due to sensitive skin. FYI, salicylic acid in high amounts is not recommended for use during pregnancy. 

How To Use Lactic Acid

Lactic acid is an AHA (like glycolic acid, below) but there are some core differences between them. Lactic acid has a larger molecular weight than glycolic acid, which means that it behaves more predictably in the skin and is slightly more gentle yet still highly effective.

The special thing about lactic acid is that it has humectant qualities too. Humectant, for all intents and purposes, means water-binding, so lactic acid helps to draw hydration deeper down into the skin.

Lactic acid is ideal for those with normal skin, dry or dehydrated skin, uneven skin tone and lines and wrinkles.

How To Use Glycolic Acid

Glycolic acid is the smallest of the AHA molecules, which means that it can penetrate deeper into the skin than others. This is a positive thing and, for some very sensitive skins, a not-so-positive thing, as it means that it is very powerful and can cause irritation in some.

Glycolic acid is best used by those with slightly thickened, sun-damaged and resilient skin. Those who are prone to congestion may see that glycolic acid can bring about pesky under the skin bumps that don’t quite come to a head, and those with dry or dehydrated skin may benefit more from hydrating lactic acid.

How To Use Hyaluronic Acid

Hyaluronic acid isn’t an exfoliating acid like the other acids mentioned. It’s actually a humectant ingredient that can hold up to 1,000 times its weight in water. We make our own hyaluronic acid in our skin, but as we age, the rate of production drops dramatically which is why it is so important to get it on topically.

There are a few different forms of hyaluronic acid, but the two ones you will see most often are high molecular weight HA and low molecular weight HA (often listed as sodium hyaluronate).

Your low molecular weight HA is the kind that can draw moisture further down into the epidermis, assisting in longer term skin hydration when used regularly. Your high molecular weight HA helps to hydrate and plump out the very surface of the skin. In an ideal world, you’d be using both of these types of hyaluronic acid.

Hyaluronic acid can be used by anyone and benefits anyone, but it is a particularly great hydrator for congestion-prone skins that don’t take well to heavier moisturising ingredients.