The truth about a suntan
There is no such thing as a healthy tan! The skin produces a dark-coloured pigment, melanin, as a shield against further damage from UV radiation. The darkening provides some protection against sunburn: a dark tan on a white skin offers a sun protection factor of between 2 and 4. However, it is no defense against long-term UV damage such as skin cancer. A suntan may be cosmetically desirable, but in fact it is nothing but a sign that your skin has been damaged and has attempted to protect itself.
There are two distinct types of tanning reaction: immediate pigment darkening occurs, where the pigment called melanin already present in the skin darkens on exposure to UVA. This immediate tan begins to fade within a few hours after cessation of exposure. Delayed tanning happens over a period of about three days, when new melanin is produced and distributed between the upper skin cells. This tan can persist for several weeks.
High doses of UV radiation kill most of the skin cells in the upper skin layer, and cells that are not killed get damaged. In its mildest form, sunburn consists of a reddening of the skin called erythema. This appears shortly after UV radiation exposure and reaches a maximum intensity between 8 and 24 hours. It then fades over the course of a few days. However, a strong sunburn may cause the skin to blister and peel, which is not only painful but also leaves the very white and new skin underneath unprotected and even more prone to UV damage.