Why is acid good for skin?
Firstly let me explain a little about the structure of the skin. The skin consists of 2 layers, the epidermis and the dermis (and a third, the hypodermis, but we can ignore that for now - if you want a more detailed explanation of the skin structure you can find it here).
The dermis sits underneath the epidermis, and is where the fibroblasts are hosted, which produce collagen & elastin to give our skin structure & support. The epidermis is the outer layer, which is continually renewing itself (every 4-6 weeks). New skin cells are generated in the basal layer of the epidermis (as the base - obvs), and as new cells are generated underneath, older cells are pushed up to the surface where they eventually die and are naturally shed, to make way for new ones. These outer dead skin cells are essentially what you are seeing when you look in the mirror.
Acids in facial skin care work by dissolving the keratin that binds the outer layer of dead skin cells (known as keratinocytes). This is great for two reasons. Firstly, it removes dead cells from the surface, which can be dull, so you reveal a fresher complexion. Secondly, this resurfacing action encourages new skin cells to be produced in the basal layer, and a faster rate of cell renewal is a good thing for our skin health.
What acids are good for the skin?
There are a wealth of acids available on the market, with it seems new ones being discovered all the time, but I am going to cover a few of the tried and tested below.
Best for: Oily-combination, congested skin types.
Why it’s special: Salicylic acid is a beta-hydroxy acid (BHA), and it’s special because it’s oil-soluble, unlike most other acids which are water-soluble. The reason that’s great is because it can penetrate into a sebum-filled pore, to remove any cell build up, resulting in less congested skin, and in turn fewer breakouts, blackheads and enlarged pores.
SkinLyst pick: Paula’s Choice 2% BHA Liquid Exfoliant
Multi-tasker: The Inkey List Salicylic Acid Cleanser
Best for: Normal-dry skin types (not sensitive)
Why it’s special: Glycolic acid is an alpha-hydroxy acid (AHA), and it has the smallest molecular weight of all the AHAs. This means it can penetrate the skin the fastest, giving the quickest results in the shortest space of time (but also makes it the most irritating).
SkinLyst pick: Alpha H Liquid Gold
On a budget: The Ordinary 7% Glycolic Acid Solution
Best for: Dry & sensitive skin types
Why it’s special: This lesser-known acid is a poly-hydroxy acid (PHA), and as such it has a much larger molecular structure, making it a gentle option for sensitive skin types. This acid has the added benefit of hydrating skin, so is a great gentle option to include if your skin is more reactive.
SkinLyst pick: Garden of Wisdom PHA Plus serum
How often should I use acids on my face?
This depends a lot on what skin type you have, and what you are using them for. For oily, congested skin, looking to address breakouts & blackheads, you can use this as much as once daily (stick to the evening).
For normal - dry skin looking to add radiance with glycolic, I would introduce a glycolic toner 1-3x week, no more. More is not more here, so play on the safe side.
For dry, sensitive skin - I would start with the PHA Plus at every other day, although this really is gentle enough for daily use, there is no harm in building up to that if you are worried about a skin reaction.
Are there any side effects of using face acids in skincare?
Whilst acids are a great ingredient type to introduce into most regimes, and have a lot of great skin benefits, there are also a few points to be aware of when introducing these.
Acids can cause initial skin purging
If your skin is breakout-prone, you may experience a ‘purge’ when first introducing them, resulting in a surge in breakouts (usually where you’re most prone), whilst the skin adjusts. You can reduce the chances of this happening but introducing to your routine slowly - starting with every 3 days and building up to once daily (if relevant) over the first 3-4 weeks.
Acids can cause skin to be more sensitive to light
Secondly, I have to point out that acids can make skin more photosensitive, meaning you need to be extra vigilant in using a broad spectrum SPF during the day. To be extra careful, I would also only use acids in the PM, and rinse off in the morning so you don’t have them left on your face during sunlight hours. For the same reason, be extra cautious during the summer months.
Acids during pregnancy
I would personally recommend to avoid all acids if you are pregnant or even breast-feeding. There is only one official guideline here as far as I am aware, which is around using salicylic acid at concentrations of 2% or higher (which is also the level it is most effective at), so definitely avoid this. I would never want to advise those who are pregnant to add acids into their regime, as this a period in life when melasma (areas of facial hyperpigmentation) is more common, due to hormonal changes. So my advice would be to avoid anything that makes your skin more sensitive to sunlight during this time to try to limit your risk (although there is no scientific evidence as far as I’m aware linking acids during pregnancy to melasma, I just think it makes sense to avoid).
The all important skin barrier
Your skin barrier is a very hard-working and essential system for your overall health as well as skin health. It stops microbes from entering the body, it stops water from evaporating, and adds some protection against pollution and UV. So we want to keep this functioning in a healthy way. Any skin acid is manipulating the skin barrier slightly, so whilst this when done right has very positive effects, we also need to be sure to include barrier-supporting ingredients in the rest of our regime (amino acids, essential fatty acids, ceramides, humectants etc). Please do not over-do it with acids, if your skin becomes irritated or dry, stop using immediately.