1. The first group of tanning pills rely on a number of carotenoids - natural pigments. It is a build up of these carotenoids in the skin that causes a colour change i.e. a tan. This tan is by no means "real," and does not offer any protection against UV exposure. This is because they do not affect the production of melanin. The colouration of the skin is only temporary and fades once the course of tablets is stopped.
The active carotenoid in these tanning pills is a substance called canthaxanthin. Once the tablet is taken the canthaxanthin is distributed through the body and is absorbed were it attaches itself to the subcutaneous layer (fat cells) that is found under the skin. This fat layer is darkened by the pigment and shows through the skin - and hey presto an instant tan!
Typically dosage is estimated on adult body weight. Below is a rough guideline:
This group of sunless tanners takes about a month to fully saturate the body, with the first glimpse of colour appearing after 1-2 weeks. When the saturation point is reached the dosage is usually halved. It should be noted that high concentrations of canthaxanthin are required to produce this change. To get around this most companies market their tanning pills as "vitamin/nutritional supplements" and not as an "oral tanner."
2. The second group of tanning pills has the active ingredient tyrosine which synthesises the production of the skin pigment melanin after and during UV exposure. The cells in the epidermis are enveloped by the pigment producing a tan. This tan is "real" and does offer some protection against further UV exposure.
Dosage usually falls in the one capsule a day mark.
The concern regarding both these groups is that the manufacturers are misleading the public luring them into a false sense of security were they wrongly believe that taking these pills will protect them from over exposure to UV and sun burn.