Langerhans Cells (from Wikipedia)

Microscopes began to be used around 1600 but it wasn’t until 1868 that a medical student called Paul Langerhans noticed some small black smudges in the skin. And it took over a hundred years before it began to be realised that what are now called Langerhans Cells are among the most amazing features of the skin.

Nothing that cosmetic science has come up with can remotely match the performance of these almost unknown little structures that look so unimportant under the microscope in this photograph of a section of the skin from Wikipedia.

When a virus is going around we take care to cover our mouths and our noses, but we rely on our skin to be an effective barrier. This is such a familiar thing that we don’t give it any thought. But viruses are really really small and should, in theory, have no difficulty penetrating the skin barrier. And in any case, the skin is full of holes in the form of the pores. Without the shield provided by the Langerhans cells viruses would have free access to our bodies through the skin.

You can’t see very clearly in the picture, but Langerhans cells have long arms that stretch out into the surrounding tissue giving them a very large surface area. They use this to grab viruses and neutralise them. They aren’t perfect anti-virus machines though. It seems that certain viruses, including the HIV virus, have been able to find and exploit a chink in their armour. Langerhans Cells are found in great numbers in genital fluids and lower numbers in the saliva. It seems they are somehow used by the HIV virus as a way of spreading. The details of how this happens haven’t yet been worked out, but it does explain why condoms are so effective in preventing the spread of HIV.

Langerhans cells originate in the blood. They start out as standard white blood cells then morph into a more specialised form. They then migrate into other tissues, take up residence and when in the the skin they grow their characteristic arms. It is these long arms which are on the look out for anything out of the ordinary that the immune system might need to deal with. When your skin reacts to something which it has come into contact with, it is the Langerhans cells that get the reaction started. The process is similar whether we are talking about a microbial contamination, a foreign chemical or a traumatic experience like sunburn.

When something that is not right is detected, the Langerhans Cells start to act. They send out messages to the body calling in the defence team of the white blood cells. At the same time they dilate the blood vessels so that there is a better blood supply to the affected area. You can often notice this by a distinct reddening of the skin. This is sometimes the only sign that anything is wrong. If the inflammatory response continues the whole skin area can puff up as it fills with white blood cells intent on fighting back the attack on the body.

I was treated to a very visual demonstration of the early stages of an inflammatory reaction the other day. I was at a family gathering on a Sunday afternoon in late April, one of the first days of the year when the weather was good enough to go out into the garden. My elderly and nearly bald father-in-law was sitting in the sun and I watched, over the space of about 30 minutes, his forehead steadily growing pinker.

What was actually happening in detail was that UV rays were falling on the unprotected skin and disrupting it. Ultraviolet radiation is high in energy and can damage anything that it hits. The Langerhans cells were detecting abnormal structures and were sending out calls for help. At the same time the blood vessels were being opened up to allow for all the extra activity, giving the reddening effect. I had been observing all this with scientific detachment, but at this stage some more sensible relatives noticed what was going on and moved the stately old gentleman into the shade.

If it had been left to me and he had been left where he was the sun damage would have increased. The specific cells which had been damaged would be identified and killed. These would then be transferred to the surface of the skin and would eventually slough off. This is quite a key activity for the skin and its defensive system. Damaged cells are quite likely to behave abnormally including becoming cancerous. It is lucky that the body is so well adapted to handle the situation.

People are sometimes surprised when they hear me saying that I am not in favour of high SPF sunscreens. Given the damage that light can do isn’t it obvious that we should give ourselves as much protection as possible? Well I am certainly in favour of protecting the skin from the sun. High energy light is just about the biggest challenge our skin faces. But I am not so sure that very high SPF products are the best way to help it.

To look at it another way for a moment, one bit of conventional wisdom I wholeheartedly agree with is to frown on sun beds. Put yourself in the position of the poor old Langerhans cell. One minute you are coping with ambient light conditions. The next you are exposed to a high energy blast of UV. I would imagine that this instigates emergency measures sending signals to react quickly to a crisis. When your session is over you are suddenly back to normal. The signals and responses that your body has evolved over millennia weren’t designed to cope with this. It isn’t surprising that this kind of stress leads to premature ageing and increased risk of skin cancer. It beats me why sunbeds haven’t been banned yet.

When you decide to apply an SPF 30 (or even above nowadays) product to your skin, you are doing something rather similar in reverse – though admittedly less extreme. This is like an overcoat. So your Langerhans cells are not remotely getting the message that you are in bright sunlight. Until that is, the SPF starts to wear off. I am all in favour of helping the Langerhans cells do their job, but to me that means a modest SPF applied frequently giving them a better chance to adjust to the situation.

I had better point out that all this is simply my opinion. I don’t have any evidence to suggest that high SPF formulations are really less effective than low ones. It is just my feeling from what I know. But it would be fascinating to compare two formulations with very different SPF values and see which one really worked the best in real world conditions in the long run. As far as I know, no such study has ever been carried out.

Another point about Langerhans cells and the way they work is that mobility is key to them. It is quite likely that they can move around more easily in well moisturised skin. Certainly the biochemical actions they undertake work better when there is plenty of moisture present. So a straight moisturiser will contribute to your ability to withstand the damaging effects of the sun. It is obvious when you think about it. And indeed, this is something that does seem to be born out by evidence. People do report less sunburn when they use moisturisers.

So there is a lot going on when you go out in the sun. And once again, the skin proves itself to be more sophisticated and more surprising than you would have ever imagined.







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