The Physics of Tanning

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Melanin is responsible for the darkening of the sun.

How is melanin produced?
When the skin is exposed to ultraviolet rays of the sun, your skin produces a special kind of skin cell called a melanocyte. Melanocytes are the skin cells responsible for producing melanin.

Why are melanocytes produced?
When the skin is exposed to ultraviolet rays from the sun, your DNA absorbs the rays. When your DNA absorbs these ultraviolet rays, however, it damages and changes its structure. This is how people get skin cancer. As a means of protecting your DNA, the body will produce cells called melanocytes which block the rays from reaching and altering your DNA.When your body has more melanocytes, you produce more melanin, thereby getting darker.

Why does it seem like you get more sun when you're by the water than tanning in your backyard?
The sun's rays are reflected and refracted by water. When you are out on the water, the sun's rays are reflected off the water, sending a second shot of UV light headed directly toward you. Additional UV light is refracted at a different angle from the water, also sending the light toward you. When you are in your backyard you absorb the light from the sun directly. When out on the water, however, you absorb not only the light directly from the sun but also the reflected and refracted light which increases your total exposure to the rays and will increase your tan (or burn if you're not careful).

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