Did you know that the natural pH of the skin surface is on average below 5, more acidic than was generally assumed?
What skin pH is
pH measures how acidic or alkaline a substance is, on a scale from 0 to 14, with 7 as neutral. The surface of the skin is slightly acidic, and this acidity helps keep the skin barrier and the microorganisms living on it in good shape.
Published values, however, varied widely, from 4 to 7. The common assumption was that skin pH sits between 5 and 6 on average. The study we are discussing set out to find the natural value, the pH of skin left to itself.
How the study was done
The researchers ran a multicenter study on 330 people. They measured pH on the inner forearm before and after 24 hours in which participants did not shower or use any cosmetics.
After 24 hours, average pH fell from 5.12 to 4.93. Based on this drop, the authors estimated that the natural pH of the skin surface is 4.7 on average, below 5. They also looked at the effect of tap water and at the condition of the skin according to its pH.
What was observed
Soaps and cosmetics used beforehand have a strong influence on skin pH. Even plain tap water, which in Europe usually has a pH of around 8, raises it for up to six hours before it returns to its natural value.
Skin with a pH below 5 was in better condition than skin with a pH above 5, according to measurements of barrier function, hydration and scaling. The study also found that an acidic pH, between 4 and 4.5, keeps the resident bacteria attached to the skin, while an alkaline pH, between 8 and 9, encourages them to detach.
How to read the result
The study is large and the measurements are simple and repeatable. The value of 4.7 is an estimate from one area of the body, the forearm, and pH can vary from area to area and from person to person.
The practical message, read with caution, is that every wash changes the skin’s environment for a few hours. Choosing gentle cleansers and not overwashing is a sensible habit. If your skin feels tight, turns red or dries out after cleansing, a dermatologist can help you find the products that suit you.
This article is for information only. It does not replace the advice of a doctor or dermatologist, whom you should consult with any question about your skin.