The Science Of Skin Typing

The effect on the skin of a melanogenic dosage will become evident only three to five days after exposure, at the earliest. Further, melanogenesis is a long-lasting process, therefore, consecutive single dosages work cumulatively. In other words, the skin does not forget the induced pigment effects and accumulates these single pigment-producing dosages over time. Besides melanogenesis, there exists the IPD, an immediate pigment darkening effect which is a rather superficially effective tanning mechanism. IPD is a transient reaction induced by the photochemical oxidation of pre-formed melanin pigments by long-wave UV, darkening the skin during exposure.

By use of a tanning unit, for example, which is characterized by an exposure time of 20 minutes for 1 MED and 45 minutes for 1 MMD, melanogenesis can be induced in two different ways.

Consider the given MMD exposure time of 45 minutes. Although the applied melanogenic dose is high enough to produce new pigments, an exposure of this duration cannot be recommended because the MED would be exceeded more than twice during such a session. The better way to get a tan will be by starting an exposure schedule consisting of three applications of 15 minutes each during one week. The advantage of such a procedure is twofold. The applied dose per session does not reach the limit of 1 MED; however, at the same time the skin has received a total melanogenic dose of
1 MMD. This means the process of new pigment formation will be induced without the risk of sunburn and the skin will remain healthier. Furthermore, at the beginning of each tanning session series, this exposure schedule is in agreement with FDA regulations.

In addition to melanogenesis, even during the first exposure session the skin will be tanned immediately if the horny layer contains some weakly colored, pre-formed pigments which then can be darkened by IPD. Generally, human skin has some pigment pre-stages available (except Skin Type I). In this context, it may be helpful to know that with most of the commonly used sunlamps, the threshold dose to initiate IPD will be reached quicker than 1 MED.

Depending on the amount of available pigment pre-stages (and on Skin Types) the effect of IPD usually remains only for hours-at the most a few days. With an increasing number of sessions, the amount of pre-stage pigment will be enhanced.

Talking about indoor tanning as well as outdoor tanning, the mechanisms of "immediate pigment darkening" and of "pigment formation" (melanogenesis) interact so that a clear differentiation between both is often impossible. As a rule, it can be established that IPD is more important during the first sessions while melanogenesis comes more and more into play during the following exposures.

By using tanning units, both mechanisms are utilized. At the beginning, the tanning results are caused mainly by IPD. With increasing sessions the obtained suntan becomes darker and deeper due to further melanin synthesis.

Further, with a well-tanned skin, the required exposure time to develop an erythema will be prolonged, and provide an effective sun protection.