July 1, 2009

Summer is now officially upon us, bringing with it the promise of long, hot, sun-filled days. Many of us will spend time outside, hoping to develop a golden tan. However, with just a little negligence, the golden tan quite easily become an ugly shade of red. Suntans and sunburns are both caused by the ultraviolet (UV) rays emitted by the sun. But what is actually happening to your skin to cause these effects?

Ultraviolet (UV) Rays Ultraviolet radiation is part of the light spectrum that reaches earth from the sun. However, it is not part of the visible light spectrum, so it is invisible to the naked eye. UV radiation can be further subdivided into three classes: UVA, UVB, and UVC. UVC is blocked by the ozone layer and does not reach the earth. UVA penetrates the skin more deeply and is the primary tanning ray. UVB affects the top layer of the skin and is the primary cause of sunburns.

Did you know? Melanocytes are specialized skin cells that produce pigment called melanin. There are two types of melanin: eumelanin (a brown pigment) and pheomelanin (a yellow/red pigment). Blondes and redheads do not tan well, because they produce more pheomelanin than eumelanin.

Suntans Tanning is actually a mechanism to protect the skin from sun damage. Pigments absorb the sun's UV rays in order to protect skin cells from damage.This is why people with darker skin (more pigment) burn less easily than people with fairer skin. Tanning occurs in two steps. Firstly, UVA radiation darkens already existing melanin. Secondly, in response to damage caused by UVB radiation, the body's melanocytes produce more melanin. Melanin production takes a few days, which is why you can't get a dark tan in one day. However, don't think that it is good idea to get a deep tan to prevent sunburn. A tan protects skin only to a sun protection factor (SPF) of 4, which means if you would normally burn in 10 minutes, an SPF of 4 would protect your skin for 40 minutes (4 times more). Moreover, prolonged exposure to UVA radiation causes skin damage, resulting in decreased skin elasticity, which leads to premature wrinkling and aging.

Did you know? A small amount of unprotected sun exposure is good for you. UVB triggers the body to produce vitamin D, which is important to help the body absorb calcium, keeping bones strong. Although vitamin D is found in some foods (especially fortified milk), many people do not ingest enough vitamin D through food alone.

Sunburns Excess UVB radiation causes direct damage to the DNA of skin cells. Our body recognizes this damage and triggers mechanisms to repair it. An inflammatory response is a complex response to harmful stimuli, in this case, damaged skin cells. By increasing blood flow to the skin through tiny underlying blood vessels called capillaries, immune cells are brought to the site of damage to help remove the damaged cells. The increased blood flow results in the characteristic heat, redness and swelling that accompanies sunburns. The damaged skin cells will release chemicals that trigger pain receptors in the skin, which is why sunburned skin is sensitive.

Did you know? The most serious effect of ultraviolet radiation is skin cancer. If the body's self-repair mechanisms cannot fix the UV-induced DNA damage,mutations can lead to skin cancer.

Don't be afraid of the sun, just take precautions to limit your UV exposure: try to avoid direct exposure to midday sun, dress to cover as much skin as possible,and apply sunscreen with at least SPF 15. Have a great summer!

Learn More:
Environment Canada UV Index Treatment for sunburns

Michelle is a PhD student at the University of Toronto studying how synapses form using the microscopic worm C. elegans as a model organism. She enjoys photography, ultimate frisbee, and crafty projects.

Michelle Po

I am currently doing a PhD at the University of Toronto in Molecular Genetics. I'm studying neuronal connectivity using the microscopic nematode Caenhorabditis elegans as a model organism. When I'm not in the lab, I enjoy playing ultimate frisbee, photography, and do-it-yourself crafty projects.

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