Effective
low pressure systems, because of the relatively low power of low pressure lamps
(typically up to 160 Watts each), use a higher percentage of UVB rays (up to
9%) than high pressure systems. The higher values of UVB do initially cause
the body to produce more melanin for a good tan, but the skin's defense mechanism
causes the skin to thicken to provide protection from the UVB. Also, the damaged
skin exfoliates so the tanned look quickly disappears. For these two reasons,
to maintain a tan on a low pressure system requires that you tan often, perhaps
as much as 3 times a week or more.High pressure tanning uses lamps of much higher power and a very low percentage of UVB. In theory there is less probability of skin damage caused by high UVB exposure and it is easier for the gentler UVA rays to provide a healthy looking tan in as little as three sessions! And with no protective thickening of the skin and no exfoliation, this tan can last for two weeks or more!