The Dangers of Tanning
Tanning is a sign that sun damage has occurred. It is triggered by exposure to both UVA and UVB light.
UVA rays are considered the dominant tanning ray. UVA light penetrate deep into the skin and can tan skin without burning. When skin is exposed to UVA radiation, sun damage is caused. The UV radiation triggers certain cells called melanocytes produces more melanin pigment, which tries to protect your cells from further damage by absorbing UV radiation from the sun. As your skin gets darker, it is a sign that damage has already occurred. Additionally, as skin darkens, it increases the risk of mutations which can lead to skin cancer.
UVB rays also contribute to tanning, but is the chief cause of sunburns and reddening of the skin. The damage inflicted by UVB rays can also lead to skin cancer.
Tanning beds are especially dangerous because of the high intensity of UV light exposure. Under natural conditions, UVA is accumulated slowly and the tanning process can take several days. Tanning beds however expose users to significantly higher doses of UVA rays. In fact, indoor tanning can increase the risk of developing melanoma by 75%.
* Source: American Society for Dermatologic Surgery