Buzz
When you spend too much time in the sun, ultraviolet rays from sunlight penetrate your skin and cells, causing damage to their RNA and DNA. This is problematic since DNA holds the essential genetic blueprints for our body's development, survival, and functioning. Such DNA damage may even contribute to the development of skin cancer. To protect you, your body responds by tanning, which involves the production of a pigment called melanin that helps block UV rays from penetrating deeper into the skin cells.
UV radiation triggers the darkening of existing melanin and stimulates an increase in melanogenesis, the process that generates more melanin. Specialized cells called melanocytes produce the pigment and release it from the cell, causing the skin to darken and absorbing UV energy, converting it into heat.
Melanogenesis results in a gradual tan that becomes visible several hours after UV exposure, and this tan tends to last longer than the darkening of pre-existing melanin. Over time, the tan will fade as layers of darkened skin are gradually replaced by newer skin cells with less melanin, eventually shedding off.
What Causes Sunburn?
We often say someone with a sunburn has been out “baking” for too long or got “fried,” but a sunburn differs from a thermal burn, like the one you might get from touching a hot stove. A thermal burn is caused by direct heat, while sunburn is the result of ultraviolet-B radiation from the sun.
When the skin is exposed to excessive UV radiation beyond its ability to protect itself with tanning, the radiation damages the DNA, as we mentioned earlier. In response, the body increases blood flow to the capillaries in the dermis (the second layer of skin) to facilitate repair. This leads to warmth and redness in the skin. Inflammatory immune cells also gather at the damaged site, causing pain and, hopefully, a reminder to stay out of the sun. Eventually, the damaged cells die, and the burned skin begins to peel off.
