I used to assess new idea proposals for a big pharmaceutical company. Smaller companies with novel ideas, products and technologies would pitch them to me and some clever but non-technical colleagues. A lot of the ideas were very involved and needed a lot of explanation. One of the things I learned from that was that any scientific idea or concept can be explained in plain English by someone who themselves understands it. Jargon is useful shorthand among people in the know, but you should be able to say what you mean without resorting to it if you need it.
This came to my mind the other day when reading a thought provoking paper entitled “Transepidermal water loss and skin site: A hypothesis” by Jonathan Hadgraft, one of the UK’s top experts of skin penetration and Majella Lane (International Journal of Pharmaceutics Volume 373, Issues 1-2, 21 May 2009, Pages 1-3, read the abstract here).
It’s an interesting and well written paper that asks the question, why is the skin on the face different to skin elsewhere on the body. But I have to say that it probably isn’t going to be a page turner if you don’t have some background in the subject matter. But as I’ve said, if I have understood it myself then explaining it to a non-specialist shouldn’t be a problem.
I think we have all noticed that the skin on our face is more sensitive than that on most of our body. What makes it different? One published paper observed that water is lost from the face more quickly than from the arm. It seems that although the skin is a very good barrier it is a less effective barrier on the face.
If you could examine the cells that make up the top layer of the skin with a really good microscope, you would see that the ones on the face are smaller than those on the arm. Another paper reports that the enzyme responsible for releasing the skin cells from the surface of the skin is more plentiful on the face. This suggests that evolution has favoured smaller skin cells on the face for some reason.
How does this affect sensitivity? Anything trying to get across the skin, either water getting out or chemicals going in, has to negotiate its way through the barrier created by the skin cells. This means that on the face the path anything trying to get into the body through the skin has to take is shorter. One way to think of it is that it is a bit like a ball bearing trying to get through a pin ball machine. The ball bearing is the molecule and the skin cells block its progress. The skin cells in the face are smaller so present less of a barrier. The face is an easier pinball table with smaller obstacles.
(Do remember though that even the skin of the face is a formidable barrier to chemicals, whether natural or man-made, getting across it. Reports that 60% of cosmetic ingredients getting into the body across the skin are complete rubbish.)
I asked for permission to include a figure from the paper here, but the publisher wanted £13 for it,. so I’ve done my own version. It took me a lot longer than I thought and should probably have coughed up the money, but here it is anyway.
The path of a chemical trying to penetrate the skin
I have blogged before that there are more pores on the skin of the face as well. So all in all the protection that the skin of the face gives you is not as good as that of the rest of the body.
Why the face should be marked out in this way I don’t know. But you can be sure that there is some selective advantage. Perhaps thinner skin allows more expressiveness on our faces. Probably humans, as social animals, survive better with a face where the skin is thin enough to more clearly communicate what we are thinking. The ability to use your face to express your emotions gives you enough of an advantage to overcome the loss of a bit of extra water.
What are the practical implications of this? Well one consideration is that you need to take more care of your face than the rest of the skin on your body. So if you have found an expensive face cream don’t waste it elsewhere. It is quite likely that the rest of your body doesn’t need it. A lot of people believe that they have sensitive skin but it could well be that all they have is a sensitive face. One last implication is for doctors and dermatologists. When people seek there advice about skin allergies they often respond with a patch test. In a patch test a whole series of chemicals is applied to patches on the back to see if they produce a reaction. This is probably okay most of the time, but if the face is much more sensitive than other parts of the body then you might miss problems that are only going to affect your face.