One thing that a lot of cosmetic companies have recently been incorporating into their marketing talk is the concept of pH and pH balance. So...
What is pH?
pH is a measure of how acidic something is. Acidity is essentially the ability of something to donate H+ ions.
- be able to donate H+ ions
- taste sour
- have a pH less than 7
If something is basic (also sometimes called alkaline), it will
- not be able to donate H+ ions easily, and in fact they'll usually absorb H+ ions
- taste bitter
- feel slippery
- have a pH greater than 7
Most things will have a pH of between 0 and 14, and substances at either extreme will be corrosive - they'll give you a chemical burn (and burn holes in other things, like your clothes!). The approximate pHs of some common substances are:
Pure water = 7
Stomach acid = 1.5-3.5
Orange juice = 3.5
Standard soap = 9-10
Shampoo = 5.5
Toothpaste = 8
Normal skin = 5.5-7
Blood = 7.4
The scientific definition of pH is
[H+] means the concentration of H+ ions.
What this means is that something that is pH 1 isn't just twice as acidic as something at pH 2 - it's 10 times as acidic! If you want to dilute a very acidic substance from pH 2 to pH 5, you'll have to dilute it 1000-fold.
So what does this mean for pH-balanced skincare?
Our skin is actually quite amazing. On the surface, there's a layer called the stratum corneum, which protects us from injury, infection and dehydration. It's made up of keratin, dead cells and secretions, such as sebum. Its pH is usually slightly acidic, but with some conditions (e.g. eczema, diabetes) the pH tends to be higher.
For people with sensitive skin, including infants and the elderly, large pH jumps can lead to interruption of the stratum corneum, leading to dryness and irritation. For the rest of us, our skin is still pretty resilient and can readjust its pH after exposure, but strongly basic soaps should still be avoided since they have more lipid-stripping power (see face washing science). Luckily most skincare companies realise this now, and most skin products are pH balanced, even if they don't say they are. In short - should you pay extra for skincare labelled with "pH balanced"? I personally don't think so!