Studies have found a possible underlying genetic susceptibility to being dependent on UV tanning.

"We observed that inherited variation in one gene - known as patched domain containing 2 (PTCHD2) - was significantly associated with whether or not young people, all of whom had previously sunbathed or indoor tanned, exhibited symptoms of tanning dependence," said Dr. Brenda Cartmel, lead author of the Experimental Dermatology study.
Source-Eurekalert