You’ve seen skin pH on packs and adverts. Should you be worried about it?
Skincare is a crowded and busy market where you have to shout loud to make yourself heard. So it isn’t surprising that just about anything you can think of has been used to sell products at some point. I don’t think there is an idea so ridiculous that somebody won’t base a skincare range on it.
But perfectly good and respectable scientific concepts get pressed into service as well. For example the notion of pH. This is something that everybody has heard about, but which is not especially well understood. In fact even chemists sometimes get caught out by it. But that hasn’t stopped it from becoming a part of many products marketing stories. Is it something you need to concern yourself with?
What is pH?
pH is all about being acid or alkaline, which ultimately boils down to hydrogen ions. Hydrogen is the smallest atom, consisting of basically a positive and a negative charge. These charges can split off in water. The positive charges are very small and fast moving so they can be very influential on larger atoms and molecules they come into contact with. The negative charges are more easily absorbed onto other atoms and molecules. The pH is in effect nothing more than a description of how mobile the negative and the positive charges are in the solution.
The behaviour of these charges in dilute solutions is very well understood by chemists, and there are very useful equations that allow the pH of some solutions to be calculated with great accuracy. This is indeed one of the great achievements of chemistry and is both intellectually very satisfying and often of great practical value.
Why pH is often important
Proteins are chains of charged molecules, and if they are water soluble can respond quite strongly to the presence of charges in the water in which they are dissolved. A good example of this is the effect you see when you squeeze a lemon into a glass of milk. Milk is stabilised by proteins that have adopted a particular shape. Putting in some acidic lemon juice wrecks the configuration of the proteins that are stabilising it. This is a dramatic illustration of the effect of pH. Water soluble proteins carry out many important processes in the body and so it is not surprising to discover that there is a mechanism in the blood that maintains the blood’s pH within very tight bounds.
So it is very reasonable to think that pH can have a big impact on biological systems. In extreme cases the effect can be very extreme – we all know to avoid getting strong acids or very caustic solutions on the skin.
Why pH often doesn’t matter
But pH is rarely the whole story. Acids and bases come in many different forms and some are much stronger than others. There are materials with high and low pH values which do very little harm – lemon juice and soap are two examples of where high or low pH doesn’t mean that it will burn your skin off.
pH and the Skin
The assumption behind the concept of pH is that we are talking about a simple solution in water. Skin is nothing like that, and in many ways the concept of pH doesn’t really apply to it. It isn’t really clear even where you would take the reading. A lot of the upper layer of the skin is comprised of a dense protein material with a very low water content indeed. There is some water in gaps in the protein, so you might consider the pH of this water to be that of the skin. But even this doesn’t really stack up that well. It is not pure water – there are lot of other stuff in there which would make measuring the pH difficult if not meaningless.
What is the pH of the skin?
Nonetheless, people are interested in the pH of the skin and attempts have been made to determine it. Figures have been published between 4 and 7. pH is famously a logarithmic scale, so that means the lowest figure is 1000 times that in the range. The differences are down mainly to different ways of measuring, and it has pretty much been agreed that the way skin pH is going to be measured is by placing a glass probe directly on the surface of the skin.
There are plenty of arguments against the validity of this particular way of doing it, but they are outweighed by it being the easiest and most repeatable. The biggest motivation for measuring skin pH is as an aid to diagnosis of skin diseases. That means you are more interested in comparing different skin samples than in the details of the science.
In fact there isn’t much to be said about skin pH from a scientific point of view. It seems to be the case that skin is slightly acidic. This has been described by some as the skin’s ‘acid mantle’. It has been speculated that the acidity is part of the skin’s defence against microbial attack. I’ve always been sceptical about this. Microbes are usually more than capable of handling pH’s as modest as measured on the skin. But there is a good chance that changing the skin’s pH by a lot might change its properties, and that those changes might have an adverse effect.
But all that really means is that avoiding things that have a big impact on the skin’s pH is a way of avoiding doing it any harm. There isn’t any particular reason to believe that the skin is in any need of helping it maintain its typical pH.
How Can You Tell When Your Skin pH is wrong?
You can’t. One of my more popular posts is how long should you give a skin cream to work and it didn’t even cross my mind to mention skin pH.
Should You Be Worried About pH?
Knowing about science is something that enhances your life, and the more you know about it the better. But that doesn’t mean it always provides a guide to action. In the case of your skin’s pH you are pretty safe leaving it to get on with managing it itself.
Reference
Natural skin surface pH is on average below 5, which is beneficial for its resident flora Int J Cosmet Sci. 2006 Oct;28(5):359-70
