Skin is the largest part of the body, which comes in contact with the sun's rays. The sun's ultraviolet rays enter the skin and help in the formation of melanin in the skin. Melanin is a liquid substance that darkens the skin. Excess of melanin in the body darkens the skin. Exposure to sun radiation also helps the body to produce vitamin D and heat.
When the body is exposed to too many ultraviolet rays, it causes a condition called sunburn. Burning due to ultraviolet rays also occurs when the body is exposed to other sources of ultraviolet rays such as phototherapy lamps, arc lamps, and tanning beds.