Going tanning twice in one day is bad. Indoor tanning is dangerous and causes potentially deadly cancers and other health issues, according to the Centers for Disease Control. It causes premature aging, can cause blindness and is especially risky for children and teenagers.
No tanning is safe, and indoor tanning is not safer than spending time in the sun, says the CDC. By design, tanning salons expose users to high doses of ultraviolet radiation in a short time. A 2010 study showed that the risk of developing the deadly skin cancer melanoma increases in direct proportion to time spent indoor tanning.
Statistics provided by the 2010 National Health Interview Survey indicate that young women make up the bulk of people practicing indoor tanning. The CDC notes that several U.S. states ban indoor tanning for people younger than 18.