Benefits
Exposure to UVB[24] light in the 295 nm to 297 nm spectra (regardless of source) leads to production of vitamin D in the skin. Vitamin D is important for a number of human functions, including the maintenance of normal blood levels of phosphorus and calcium and the promotion of healthy bones. Studies have shown that many people don't get enough of the vitamin, which may even aid in the prevention of cancer, diabetes, and HIV.[25] However, because tanning beds use bulbs that emit mostly UVA light (95% UVA and 5% UVB), tanning beds do not appreciably help the body produce vitamin D.
Tanning makes most people feel good. To understand how this happens, researchers set out to determine if endorphin levels were increased after tanning. They concluded that there were no significant differences in the mean plasma levels of β-endorphin between people who were exposed to tanning beds and those who were not.[26] The positive psychological benefits of tanning may be due to factors other than endorphins.
It is believed that indoor tanning beds are useful for the treatment of SAD (Seasonal Affective Disorder),[27][28] though this is disputed at present.[29] It is plausible that the benefit that many SAD patients experience are more due to tanning causing them to feel good in general, rather than treat the SAD itself.
While a tan that is developed in a tanning bed does offer some protection from overexposure to the natural sun, it is more cosmetic than a natural tan. A tan provides a natural SPF of between 2 and 4. Depending on the intensity of the sun outside, it may be advisable to use additional lotion with SPF even if a base tan is present.
A more controversial benefit of tanning indoors rather than tanning outside is the amount of control the tanner has. If a person decides to get a suntan and wants to minimize the risk of getting a sunburn, a tanning bed offers an environment that delivers virtually the same amount of UV in a given period of time, day after day. In contrast, the amount of UV that reaches the ground can vary from minute to minute and the longer tanning times results in deeper exposure. This doesn't make the tan in a tanning bed safer per se, but it can reduce the chance of a sunburn.
One of the most commonly mentioned benefits of tanning in a tanning bed is time savings. Most tanning beds offer a maximum session time of 20 minutes. After a desired level of tan has been achieved, a person can maintain that level of color with typically 1 to 2 sessions per week, which can often be accomplished in a lunch hour. For individuals living in urban areas, or who work extended hours, a tanning bed may be the only opportunity for tanning or UV exposure of any kind.
Compared to tanning outside, other benefits include comfort, available of tanning even if it is cloudy or late at night, tanning inside is cooler than in the hot sun, you don't get tan lines if you decide to tan nude, and socialization. In many communities (particularly smaller towns), the tanning salon is a social place, like a hair salon (and sometimes both are the same place) and offers stay-at-home parents an opportunity to get out of the house and socialize.
Medical Use
Some people with psoriasis or eczema are treated with UVB light therapy (known as PUVA, for Psoralens and UVA radiation) to lessen the symptoms.[30]. This is typically in the 310 nm to 315 nm portion of the UVB spectrum. Virtually all fluorescent tanning lamps have one spectral peak within this region of the UVB spectrum, making them an effective tool in mild to moderate cases. In some circumstances, salon memberships have been prescribed and more rarely the purchase of home tanning beds have been prescribed by doctors and may be covered by insurance policies. Tanning may temporarily help some forms of acne by drying out the skin, but it is not a solution that lasts for very long.[31][32][33] Further, most prescription or over the counter acne medications (e.g. Accutane, Benzoyl Peroxide, Retin-A) should not be used in combination with ultraviolet exposure or the user may experience negative side effects from burning to delayed healing due to photosensitivity that these drugs (and many others) can create.