You should always wear a sunscreen, 365 days of the year, even on cloudy days. The UVA portion of the spectrum is constant all year round, regardless of how sunny it is outside. And UVA is the main cause of skin damage.
UVA consists of longer wavelengths and therefore penetrates deeper into the dermis than UVB rays, damaging DNA in cells and collagen & elastin fibers. (The dermis is 70% collagen.) The end result is wrinkling, sagging, and potentially skin cancer.
UVB also causes DNA damage but because the wavelengths are shorter, they will inflict damage first in the epidermis, then gradually penetrate into the dermis.
For this reason, UVA is typically called the ‘aging ray’ and UVB the ‘burning ray.’ 85-90% of aging is due to photo damage from UV.
The ozone layer filters out much of UVB, but the vast majority of UVA goes right through clouds and window glass. So if you are indoors near a window, you will be exposed to UVA. That is another reason to wear sunscreen every day.
Also a good idea to stay away from tanning beds, which use UVA light.
by Rita Lee. Eclectic! A biochemist by training, former marketer, serial startup’er, licensed esthetician, beauty entrepreneur, Harvard alum, and global nomad. I’m on a mission to teach people about skin and improve the delivery of skin care. I blog about skin care at: JustAboutSkin.com. Read more on Quora.
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