Any physical environment, whatever its nature (except if it does not contain water), may be characterized by its degree of acidity or alkalinity, measured by its pH (potential of Hydrogen). And the skin is no exception, so cosmetics must take this into account not to risk damaging it. Everyone can identify their skin pH to choose products that suit them.
The pH is measured with a range from 0 (very acid) to 14 (very alkaline). A pH of 7 (that is the pH of pure water at 25 °C) is considered neutral.
The skin is usually slightly acid, which helps it develop more efficient protection against the natural, permanent attacks of the micro-organisms it is in contact with on a daily basis. When it is healthy, its pH is most often between 5.0 and 5.5.
This natural protection is built over time, little by little: the skin pH of a baby is close to 7, and then it reaches about 5.5 at puberty.
Therefore, the pH of ‘normal’ skins is close to 5.5, while dry skins are more acid (pH < 5.5), and oily skins more alkaline (pH > 5.5).
pH in cosmetics
When its balance is disrupted, in particular due to the contact with an environment with a different pH, the skin needs more or less time to restore it. Over this period of time, its defences are harmed: the pH modification may result in the skin flora being damaged, which makes it less resistant to infections or the proliferation of pathogenic germs… hence the importance for a cosmetic product to get closer to the pH that will be the most compatible with that of the epidermis, which it is supposed to nourish or cleanse. This criterion seems quite difficult to satisfy: for example, the pH of traditional soap equals about 9 or 10. That is why the cosmetics industry uses pH regulators or works on more acid formulas, like that of syndets, which are less damaging for the skin. On the contrary, certain types of products, like liniments for babies or skincare products for oily skins, intentionally have a more acid pH to better regulate the skin, or others, like depilatory products, must be very alkaline to be efficient.
How to recognize a skin type
Measuring the skin pH is not necessarily that simple for everyone. To determine your skin type, the easiest ‘trick’ is still to carry out the ‘silk paper’ test.
After thoroughly cleansing your skin, wait about 30 minutes, so your skin has enough time to restore its balance. Then, apply a silk paper sheet (like toilet paper) on the central part of your face (forehead, nose, chin), and another on a cheek for a few seconds (without rubbing).
You can actually ‘read’ the result:
• If both sheets are a bit damp, it means they have absorbed some sebum: your skin is oily and, most often, it looks shiny and its pores are dilated
• If the sheet in the middle is slightly stained, but the other looks intact, you have a combination (or normal) skin, a little oilier on the nose and forehead, but without any problem anywhere else
• If both sheets bear no trace, your skin is rather dry: it is often thin, sometimes rough, it easily feels a bit tight, and it has a few fine lines
N.B.: few cosmetics labels display the product’s pH. The most generous companies in terms of information are often content to specify the pH is ‘neutral for the skin’. But even in this case, the product might trigger irritations and discomfort, especially if the skin is also sensitive or reactive…