The sun warms our planet, powers photosynthesis and even helps you manufacture your own Vitamin D3. You couldn't exist without it, but when it comes to aging the sun is, by far, your skin’s worst enemy.
The sun emits radiation in all directions, a small portion of which hits the earth, and a tiny fraction of that may hit your skin. The dangerous part of solar radiation is ultraviolet: in-between the violet end of the visible spectrum of light and x-rays. Three different kinds of UV radiation are emitted by the sun: UVA, UVB and UVC.
Solar UVC radiation is the shortest wavelength and therefore highest energy of the UV spectrum emitted by the sun. It would be hugely damaging to your skin, but luckily atmospheric oxygen and the ozone layer block UVC, protecting you from it completely.
Solar UVB radiation is longer wavelength and lower energy than UVC. Most of it is blocked by the atmosphere or is absorbed by clouds, airborne pollution, glass and clothing. UVB is the segment of UV radiation that causes sunburn and, as you know from the UV index, its intensity changes with the time of day, the seasons and even your altitude.
Up to 70% of the UVB that does reach you is reflected by your own skin. Less than 30% of incident UVB affects the outer, mostly dead, layer of your skin (your epidermis). About 10% of the UVB that falls on your skin reaches your deeper, living layer (your dermis). Despite all of these things that deflect UVB it's the segment of UV light that skin cancers have been historically attributed to.
Solar UVA radiation is the longest wavelength of the UV spectrum and therefore the lowest energy. Unfortunately it is the most efficient at penetrating potential obstacles like our atmosphere, glass and your skin.
Because it's not easily deflected, the intensity of UVA radiation isn't heavily dependent on where you are, the time of day or the amount of cloud cover. As long as the sun is up, most of the UVA heading in your direction is getting through.
Of the solar UVA radiation that manages to reach your skin about 80% penetrates through your epidermis to the deeper layer of skin (your dermis) and the remaining 20% penetrates further still. In fact, according to measurements, up to 90% of the total solar UV energy that affects your unprotected skin is in the UVA segment.
The point of all this: plenty of UVA is not getting stopped by those clouds, that rain or even that glass in your windows. This is why UV protective sunglasses, hats, protective clothing and broad-spectrum sunscreen are so important.
On a side note; most tanning beds avoid burning your skin by emitting predominantly UVA. According to the US Skin Cancer Foundation "Frequent tanners using new high-pressure sunlamps may receive as much as 12 times the annual UVA dose compared to the dose they receive from sun exposure". So if you're thinking about visiting a tanning salon please be mindful of the dangers!
All of this radiation has consequences, so here's the most important statistic about photodamage:
“It is generally accepted that up to 85% of the visible skin changes commonly attributed to aging are caused by chronic [long-term, every day] solar exposure. With proper protection from UV radiation, most premature aging of the skin can be avoided.”
Taylor, C.R. et al, Photoaging/Photodamage and Photoprotection, J Am Acad Dermatol, 1990: 22: 1-15
To be clear: based on a scientific study it is estimated that around 85% of what we recognize as the symptoms of aging are a direct result of cumulative exposure to UV (usually from the sun). In other words all of those other factors that we know cause aging like repeated facial movements, bad skincare, smoking, poor diet, stress etc. account for only around 15% of the visible changes associated with aging skin.
When sunlight reacts with unprotected skin, free radicals are released. In the absence of antioxidants to squelch them, the free radicals cascade through your tissue leaving a trail of collateral damage. Your body responds to tissue damage by becoming inflamed and healing itself. But if this condition is not resolved it can turn into chronic (long-term) inflammation in which your own immune system attacks healthy cells.
Chronic inflammation in skin often results in production of collagenase, elastase and hyaluronidase: natural enzymes that attack healthy collagen, elastin and the 'ground substance' that plumps them. This causes your skin to lose firmness and elasticity resulting in fine lines and wrinkles; two of the main signs of aging.
UV exposure can also trigger uncontrolled production of melanin causing darker spots on your skin commonly known as sunspots. Sunspots (aka solar lentigenes) are another primary sign of aging skin.
If these facts sound dire the conclusions we should all draw from them are a lot more nuanced.
First, these facts all relate to exposure of unprotected skin to UV light. An SPF30 sunscreen can protect you from 97% of the UVB that manages to reach your skin. If it has been designated as 'broad-spectrum' it will also provide 'similar' protection against UVA. If you apply sunscreen, and more importantly re-apply as directed, you will already be avoiding most of the damage that the sunlight could be doing.
When re-applied regularly:
An SPF 15 sunscreen protects your skin from 93% of UVB radiation
And an SPF 30 sunscreen protects your skin from 97% of UVB radiation
Sunscreen: The Burning Facts, Published by the US Environmental Protection Agency: pdf file
Second, everything we understand about damage from the sun shows that the cumulative effect of exposure is the root of skin damage. In other words it's more important to form sensible habits around protection and prevention of daily exposure, than it is to worry about short periods of unprotected exposure. We've found that the most helpful step toward developing a habit of daily sunscreen use is to find a sunscreen that you actually like to use. If you find your sunscreen unpleasant, you simply won't use it every day.
Lastly, every cloud has a silver lining, perhaps it is this. Now you know that up to 85% of what may age your skin is UV exposure, you are in a position to do something about 85% of what will age your skin. It's time to take control!
Enjoy your time in the sun, limit it where possible and most of all be safe out there!
Thanks for reading!
ALEXIARES & ANI