Tanning Beds vs. Natural Sunlight

Tanning beds have a different ratio of UVA to UVB radiation than sunlight does. Furthermore, the radiation levels are more intense, requiring individuals to limit their exposure to very brief periods. One unanswered question is: what is the effect on the human body when it is forced to absorb such a large amount of UVA radiation in such a short amount of time? For example, one study found that the amount of UVA radiation, which penetrates deeper into the skin, was anywhere from about 3-8 times greater in the tanning beds than in the light from the sun.
While there appears to be a link between indoor tanning beds and cancer, the connection is not possible to indisputably prove because people who tan indoors also tan outdoors. Furthermore, cancer shows up decades after exposure. Last, there is a genetic component to skin cancer. None of this changes the fact that there are risks associated with exposure to UVA and UVB for anyone who is exposed for any length of time, regardless of whether or not they burn (see above for the description of the process by which ultraviolet light damages DNA).
Last, while living in a constantly sunny climate may confer some benefits, intermittent exposure to strong sunlight may be more important in the etiology of melanoma than chronic long-term exposure. Therefore the "weekend" tanner and the tanner vacationing with its increased UV radiation are all at greater risk due to the intermittent nature of such exposure.