The main ingredient is DHA
The self tanning industry uses DHA (dihydroxyacetone) as the ingredient that makes the magic happen in the self tanning process. DHA is a natural sugar that reacts with skin proteins, including amino acids, in the outermost layer of the skin. The reaction develops brown skin colouring that looks very similar to a natural tan.
Skin colouration takes anywhere from two to four hours to develop and lasts approximately 4 to 7 days. This depends on the skin type, the DHA concentration (known as the the %) and the preparation to the skin prior to spraying. The tan fades as the dead layers of skin slough off, just as in a normal tan.
Skin is made up of two main layers
The epidermis on the outside and the dermis on the inside. Whether you are talking about sun tanning or fake tanning, the epidermis is where the action occurs. The epidermis is also made up of layers. The deepest layer of the epidermis, called the stratum basale (basal layer), is affected during sun tanning. The stratum corneum (horny layer) is the outermost layer of the epidermis — it is this layer that is affected by most sunless- tanning products.
Every day, millions of dead skin cells are sloughed off or worn away from the surface of your skin. In fact, every 35 to 45 days, you have an entirely new epidermis. This is why tans from sunless- or self-tanning lotions will gradually fade – as the dead cells are worn away, so is your tan.
UVA and UVB Rays
It’s important to remember that unless the product contains an added sunscreen, it will not protect you from the sun’s UVA and UVB rays. Even products that do contain a sunscreen won’t be of much help, since they lose their efficacy within hours of application. So, if you’re planning to head outside to show off your new glow, be sure to apply some extra sunscreen.