To understand the tanning process, we need to understand a little bit about our skin. Skin is made up of two main layers: the epidermis, which is the outer layer and the dermis, which is underneath.
The epidermis itself is made up of layers, the deepest of which is the "basal layer", and it is in this layer that 'melanogenesis', the tanning effect, is produced. The "horny layer" is the outer layer of the epidermis and this where most tanning pour-on products are active.
There are many tanning accelerators and sunless tanning products available today, from pour-on lotions to tanning pills. Tanning pills in particular usually come in two forms, those that produce an artificial tan and those that support the body's production of the brown pigment, melanin.
Usually both of these types of products include other minerals and vitamins that may help protect the body during exposure to UV light.
Many users suggest that the most effective pour-on sunless tanning products are self-tanning lotions that contain dihydroxyacetone (DHA) as the active ingredient. DHA is a colourless sugar that interacts with the dead cells located in the horny layer of the epidermis. As this interaction occurs it results in a colour change which lasts for about five to seven days. Every day, millions of dead skin cells wear away from the skin's surface.
As our epidermis naturally renews itself every 35-45 days, sunless or self-tanning lotions will gradually fade as the dead cells wear away. For this reason, most of these products recommend that you reapply the self-tanner about every three to four days to maintain your "tan" to prevent it from become patchy.