I remember something from my anatomy and physiology class. I can't remember if they were a type of skin cell or pigment or whatever. Anyway, you have these two cells (we'll just call them that for our current purpose because I think that's what they were anyway) in your skin. The sun rays kill off one type, but do not harm the other type which is able to make repairs and replenish the other type of cell. Tanning beds kill off the other type of cell so that when you go out in the sun and have the first type of cells killed off, the cells that make repairs are gone and cannot repair or replenish the other type of cell. The first type that the sun kills is not able to make repairs or replenish. Anyway, you get the jist. Ever since I learned this, I just tan in the sun because it's much healthier.