Our skin has a natural protective barrier called the acid mantle. This is a fine layer of sweat that carries small amounts of bodily acid, excreted through the oil glands. Acid is anything below a pH level of 7 (neutral), as opposed to above 7 (alkaline) on the pH scale.
Once this sweat evaporates, all that is left is the acid layer, known as the acid mantle. This layer can naturally fall anywhere between a pH of 4.5 to 6.2.
What does the acid mantle do?
Our acid mantle protects the inside of our bodies from bacteria. This works because human blood is alkaline (around a 7.4 on the pH scale). Pathogens have usually evolved to only exist in a very narrow pH range. Because our skin’s pH is so different to that of our blood, bacteria which can survive on our skin and enter our bloodstream are unsuitable to our internal pH, and the bacteria that would theoretically thrive in our alkaline blood are unable to breach this acid mantle at all.
What does the acid mantle have to do with skin health?
The acidity of our skin, along with healthy oil (sebum) production and natural exfoliation of old skin (desquamation) all work together to deter bacteria which cause common skin conditions like acne, or in some cases rarer ones like MRSA infections. Those who suffer from barrier defects like sensitivity and eczema are commonly found to have a weak acid mantle and skin with a high pH.
By using products that are of a balanced pH (that is to say, slightly acidic like our skin), we do not disrupt our skin’s defence mechanism. This keeps it healthy and functioning to the best of its natural ability.
It’s essential that products you’re using on your skin – like cleansers, toners and moisturisers – are pH balanced. Some do this nicely, and others not so much.
What can I do to keep my skin at the correct pH?
Here’s two easy, cheap ways to care for your acid mantle and keep your skin’s pH in the healthier range.
1. Avoid putting anything alkaline on your face
Often, the culprit behind dry, irritated skin and a damaged acid mantle is our cleansers. Anything with a pH of 6.5 or higher is too alkaline for our skin.
This means NO BAKING SODA and NO MILK OF MAGNESIA. I’m looking at you, Instagram “gurus” and Pinterest DIYs. Baking soda is often touted as a wonder exfoliant and cure-all for those with acne or other skin issues. This is absolutely not true. With a high pH of of 8-9, baking soda is not a safe ingredient for skin health.
The problem arises when baking soda’s unbelievably high pH comes in contact with your naturally acidic skin. It essentially neutralises your acid mantle, allowing harmful bacteria to multiply in the hours following your ‘scrub’. If anyone tells you that using baking soda on your skin is great for whatever reason, run far, FAR away.
Skin care minimalists won’t like to hear this, but nothing alkaline also means no bar soap. The soap manufacturing process utilises lye, almost the most alkaline thing you can get your hands on, with a whopping pH of 13 (that’s 10,000,000x more alkaline than your skin!). The final bar product usually falls at around a 9 or a 10 – similar to baking soda – and is bad for the same reasons, even when it’s made out to be some sort of miracle product (cough African Black Soap cough).
On top of this, soap is a very effective remover of oils and grease, which is (perhaps surprisingly) not a great quality for a facial wash. This irritates and sensitises the skin, leading to tightness and dehydration and sensitivity. We want to gently cleanse the dirt from our face, not dry it out.
(Also extrapolate this instruction to all acidic foodstuff: like the ever-popular lemons, apple cider vinegar, etc. They are too acidic to be used neat.)
So what should you wash your face with instead?
2. Use a dedicated facial cleanser that has a pH of 4.5-6
This tip sounds scary, but you can find a huge list of cleansers alongside their pH levels over on Skincare Dupes. Shoot for something in this range and you’ll be a huge step closer to healthy happy skin!
Those with dry or dehydrated skin might try something creamy like Neutrogena Ultra Gentle Daily Face Cleanser, while more oily skins or those who just prefer a foaming texture could try Cerave Foaming Facial Cleanser or Simple Kind To Skin Refreshing Gentle Wash Gel.
All of these are easy to find and affordable, but most importantly fall within a safe pH level range. Don’t trust claims on the bottle like ‘pH balanced’ or ‘for sensitive skin’ – these aren’t regulated and are often misleading.
For the science geeks among you, here is some more reading on the science behind skin & pH:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4171909/
https://books.google.com.au/books?id=AWEDzXOAivgC&pg=PA31&redir_esc=y#v=onepage&q&f=false
https://link.springer.com/article/10.1007%2FBF00412626
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