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Most people know that sunlight contributes to wrinkles and skin aging as well as increases the risk of skin cancer. What most people don't know is that many sunscreens do not protect from skin aging and that staying out of direct sunlight will prevent only part of sun damage. Since sun damage is partly irreversible, it should be prevented as much as possible. This article aims to clarify some common misconceptions about sun damage.
The reason sunlight and tanning beds are bad for your skin is ultraviolet radiation (UV-light or UV-rays for short), which represents a small but important portion of the sunlight spectrum. UV is a killer of living things: it can damage almost any part of the cell, but especially its blueprint, the DNA. Suntan, which is the accumulation of UV-blocking pigment melanin, is a defense mechanism whereby the skin tries to protect itself from destruction. There are three subtypes of UV light: UVA (400 nm wavelength), UVB (320 nm), UVC (100 nm). UVC is almost completely absorbed by the ozone layer and does not reach the Earth's surface. So, as long as we haven't destroyed the ozone layer, we don't have to worry about the UVC. But we do have to worry about the other two. UVB causes sunburn, but has a relatively modest effect on skin wrinkles because most of it is absorbed in the epidermis (the outer skin layer) and does not reach the dermis where wrinkles form. UVA penetrates deeper into the skin and is the major contributor to skin damage and wrinkles. Both UNA and UVB can contribute to the development skin cancer.
An ideal sunscreen should protect from sunburn, skin aging and skin cancer. To do that, a sunscreen must provide a high degree of lasting protection against both UVA and UVB. It is relatively easy to figure out a sunscreen's effectiveness against UVB: if you spent some time in the sun and have no signs of sunburn whatsoever, then you probably have a good UVB sunscreen. An even better way, at least in theory, is to look at the sunscreens SPF (sun protection factor), a number indicating the degree of protection against UVB. A sunscreen with SPF 15 or higher should provide a good UVB protection as long as it stays on the skin long enough.
UVA is much more problematic. You cannot detect UVA damage without special equipment (such as Wood's lamp). And there is no SPF-like number to grade UVA protection. Rarely, sunscreen packaging will include the percentage of UVA it blocks. Anything above 90% should be satisfactory. In most cases, you just have to look for ingredients known to block UVA, which include so-called physical and chemical UV blockers. Physical blockers are finely powdered and dispersed minerals and include zinc oxide and titanium dioxide. To be precise, these physical blockers filter out both UVA and UVB. Chemical UVA blockers include avobenzone (a.k.a. Parsol 1789 or methoxydibenzoylmethane) and Mexoryl, a newer, seemingly more effective UVA blocker developed in Europe. Finally, there is Tinosorb, a good UVA+UVB chemical blocker approved for use in clothing but not on the skin.
No single sunscreen is perfect for everyone. Chemical sunscreens are invisible but may be irritating, degrade over time or dissipate quickly. Physical blocking agents are more stable and less irritating because they are inert. On the other hand, they produce a matte look, may clog pores and may be easier to rub off as they do not penetrate the skin. Notably, a recently developed transparent form of zinc oxide Z-Cote is claimed to offer the best of both worlds: broad UVA+UVB protection, stability and transparency.
Limitation of sunscreens
Even the best UVA+UVB sunscreens do not provide full protection. First, some UV rays still manage to get through. Second, it is easy to accidentally rub off, wash off or sweat off much of your sunscreen. Third, it is easy to forget to reapply sunscreen as often as recommended. It is fun to be in the sun. But it is fun to look young too. Limit your sun exposure even when you are wearing sunscreen.
When outside don't assume that wearing a hat or staying in the shade protects you from UV light. Reflected light may retain over a third if its UV rays. When outside always wear a UVA and UVB-blocking sunscreen. You may have heard that glass blocks UV rays. It does block UVB quite well but fails to block much of UVA. This means that in a room brightly lit with daylight you still should wear sunscreen to ensure maximum UV protection.
Downside of light avoidance
Some people choose to stay out of the sun and bright daylight altogether. This is clearly a solution for minimizing UV damage but it does have some downside (besides reducing the enjoyment of life). In some people, lack of exposure to bright light may disturb normal sleep-wake cycle leading to insomnia and depression. This has to do with the effect of light on the production of some brain chemicals, such as serotonin and melatonin. Sunlight is also needed for the body to produce vitamin D whose deficiency leads to bone loss and poor immunity. If you have no sun exposure, make sure that you get 100% RDA for vitamin D in your vitamin supplement or in vitamin D fortified milk.
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