Sunburn - Cause

Cause

Sunburn is caused by UV radiation, either from the sun or from artificial sources, such as welding arcs, the lamps used in sunbeds, and ultraviolet germicidal irradiation. It is a reaction of the body to the direct DNA damage, which can result from the excitation of DNA by UV-B light. This damage is mainly the formation of a thymine dimer. The damage is recognized by the body, which then triggers several defense mechanisms, including DNA repair to revert the damage and increased melanin production to prevent future damage. Melanin readily absorbs UV wavelength light, acting as a photoprotectant. By preventing the disruption of bonds that higher energy photons can produce, it inhibits both direct alteration of DNA, and generation of free radicals, thus indirect DNA damage.

The pain may be caused by overproduction of a protein called CXCL5, which activates nerve fibres.

Experiments with mice found that protection against sunburn by chemical sunscreens does not necessarily provide protection against other damaging effects of UV radiation such as enhanced melanoma growth.

Skin type determines the ease of sunburn. People with fair or freckled skin, blond or red hair, and blue eyes have a higher sunburn incidence. Age also affects how skin reacts to sun. The skin of children younger than 6 and adults older than 60 is more sensitive to sunlight.

Factors of sunburn include:

1. The time of day. Between 10am and 4pm daylight saving time, the sun's rays are the strongest. Even on a cloudy day, the sun's damaging UV light can pass through clouds.
2. Proximity to reflective surfaces, such as water, white sand, concrete, snow, and ice. All of these reflect the sun's rays and can cause sunburns.
3. The season of the year. The position of the sun on late spring and summer days can cause a more severe sunburn.
4. Altitude. At a higher altitude it is easier to become burnt because there is less of the earth's atmosphere to block the sunlight. UV exposure increases about 4% for every 1000 ft (305 m) gain in elevation.
5. Proximity to the equator (latitude). The closer to the equator, the more direct sunlight passes through the atmosphere. For example, the southern United States gets 1.5 times more sunlight than the northern United States.
6. The UV index of the day, which shows the risk of getting a sunburn that day.