A local ad says: Come get a base tan to protect yourself before vacation. Although tanning beds emit few UVB "burning" rays, which burn the outermost layer of skin, they do emit UVA rays, which penetrate deeper. This causes permanent damage to the skin and immune system, and skin cancer, including deadly, malignant melanoma. I was diagnosed with actinic keratosis in my 20s. It's ugly and precancerous. Studies by the Cancer Institute show that those who use indoor tanning are 2.5 times more likely to develop skin cancer than those who don't. The claims that a "base tan" will protect you are false. You can still burn, and since the UVA rays cause thinning of the skin, it can actually lessen your resistance to damage.
The claims that beds are a good source of vitamin D are almost comical. There are safer sources. Don't kid yourself. It's not safe, period. Why not get your tan from a bottle?