Whenever you decide to clean your house, you could be slowly but surely sweeping your tan right out the door.
Walk along a California beach on a warm summer day, and there are sure to be dozens of men and women, spread out on their towels, soaking in as much sun as they can. Sure enough, about six months later, in the cool months of January, February, and March, that same tan they worked so hard to obtain is... gone. What happened?
The short answer: it fell off.
The long answer? Let’s start with how we tan. Put simply, a tan is a protective mechanism for the skin according to Dr. Ali Hendi, a skin cancer specialist from Georgetown University.
There are a few cells in the basal (bottom) layer of the epidermis (or outer layer of skin) called melanocytes which produce a pigment called melanin. These cells are interspersed within the skin and make up about 1 percent of the skin. Dr. Hendi compares them to octopuses with little tentacles delivering packets of melanin to surrounding skin cells. “The job of the melanin is to protect the skin, specifically the nucleus,” Dr. Hendi says. “It sits right on top of the nucleus almost like a little cap.” The “cap” of melanin on top of the nucleus helps protect the skin from UV radiation by absorbing some of the excess rays, which can cause mutations in skin cell DNA that can lead to skin diseases.
For the rest of the story: http://www.popsci.com/science/article/2013-06/fyi-why-do-you-lose-your-tan-winter?src=SOC&dom=tw