Your skin’s own defense strategy
Hello Beautiful! Despite red hot evidence to the contrary, your skin is actually remarkably well equipped to deal with the damaging effects of UV rays. But then again, the sun is responsible for much more than sunburn and premature aging-happily not all of it negative.
In fact, our skin is extraordinarily capable both at fending off attack and of repairing much of the injury inflicted. For the most part, it performs an exemplary life-long role of protecting us from the outside world. That it becomes wrinkled and blotched in the process. Wrinkles and age spots don’t kill, nor do they ever seriously affect our general health. If wrinkles were a life threatening condition, you can be sure that evolution would be working on weeding them out. Even skin cancers, the incidence of which is, worryingly, steadily rising, are rarely a problem before our sixth or seventh decade. Until a few year ago, we couldn’t reasonably expect to live long enough to see skin cancer develop, let alone see it endanger our lives.
There are a number of complex mechanisms by which our skin protects itself from ultraviolet rays, the very first of which is sebum. Some UVB rays don’t even get past our oily outer mantle because sebum itself blocks them- another reason why oily skins are better equipped to cope with the sun. What does get through induces skin to protect itself by 1) thickening or by 2) tanning.
After several days of UVB exposure, your stratum corneum thickens considerably-up to six times its normal depth. If you are still horrified by the seeming inadequacy of your skin to cope with the sun you may be reassured to know that a well thickened stratum corneum absorbs or reflects up to 75% of UVB. This thickening does not occur with UVA radiation which is why sunbeds are not a worthwhile pre-holiday prophylactic measure. Because they are almost dead anyway, anucleic, keratin-filled stratum corneum cells are relatively unaffected by they UVB they absorb.
Note: You should be aware that if you use active skincare products which are formulated to smooth and refine the situation the stratum corneum (eg AHAs and retinal or retinoid-based creams) you will be removing some of this natural protection. You should therefore be particularly assiduous in your use of sunscreen.
As and when the ultraviolet light frazzles a section of DNA, excisor enzymes are dispatched to snip out the botched bit and make way for a perfect new piece. The duplicate piece which arrives to take its place is called a thymine dimer. It is the presence of this dimer which sparks the melanocytes into action. Melanocyte stimulating hormone (MSH), which is already circulating, waiting for the call up, begins to bind to the melanocytes. The spiky arms of these dentritic cells grow and branch out, each eventually touching about 36 keratinocytes. Then tyrosine, the melanin pre-cursor is brought into play and courtesy of various enzymes, is turned into melanin. Pockets of melanin are incorporated into organelles called melanosomes and then packed off to take up residence in the surrounding keratinocytes (epidermal cells). There they form a physical umbrella over the cell nucleus to prevent radiation falling on the DNA and RNA. Some melanosomes, meanwhile, hang around in the spaces between cells to help mop up pillaging free radicals.
Neither toughening nor tanning happens immediately. It takes several days of repeated exposure for your outer skin to build up, 36 hours for the first of your melanin to be produced and about three weeks before it reaches its protective plateau- something to remember on the first few days of your holiday.
Both of the above defense mechanisms concern the epidermis only. It is reasonable that the skin puts it most determined efforts into fighting UVB (and short wave UVA. After all, only they can cause life threatening, cancerous changes. It does mean, however, that you will have to step in to protect your skin from longer, prematurely aging UVA rays. Further damage limitation occurs in both epidermis and dermis in the form of free radical scavenging. S number of natural anti-oxidants (superoxidedismutase, glutathione, melanin) are on hand, ready and willing to sacrifice bits of themselves to free radicals generated by the sun.
These naturally-occurring anti-oxidants are extraordinarily powerful. However, they are very quickly exhausted by ultraviolet radiation-after twenty minutes of exposure, levels of glutathione, for instance have markedly fallen, the more we find out about how good natural anti-oxidants are, and about how quickly they are used, the more skincare companies are attempting to build extracted or synthesized versions into there sun and after-sun products.
When you are young your skin’s defense and repair mechanisms work at full efficiency. But as you age, it’s ability to keep up with the maintenance slows. There comes a point when, if the level of damage exceeds the potential for repair, regeneration turns to degeneration. This is the point when UV damage begins to accumulate, the end result of which is weathered, wrinkled skin.
Next time, we will talk about sun-sensitive skin.