The Science Of Skin Typing

MED is the Minimal Erythemal Dose and is defined as the threshold dose that may produce sunburn. MMD, on the other hand, is the Minimal Melanogenic Dose and is equal to the lowest dose required to develop a visible suntan. Even though the terms MED and MMD seem to be self-explanatory at first glance, the translation of these values in the daily practice of indoor tanning often leads to misunderstandings of wrong interpretations, especially when it comes to determining exposure times based on MED and MMD values.

Assume that unprotected skin has been exposed to UV radiation for the first time. In order to determine the MED, the reaction of the skin will be recorded 24 hours after exposure. The minimal dose that induces any visible skin reddening at that point of time is defined as 1 MED. Redness that occurs immediately after exposure and disappears during the following three to five hours is caused mainly by heat and is not comparable with real UV erythema. This is the reason why the reading is not taken until 24 hours later.

For users of tanning units, the MED provides important information about the sunburning effect of the equipment, since an even perceptible reddening is the first sign of a sunburn reaction. In order to prevent possible acute or long-term risks due to indoor tanning, the MED should not be exceeded during a session.

The MMD is determined in a very similar manner. In contrast to the MED examination, the readings are performed seven days after exposure instead of 24 hours. The minimal dose required to produce an even noticeable tan, which can still be observed seven days later, is defined as 1 MMD. The interval between exposure and reading is necessary to permit the occurrence of new melanin biosynthesis (melanogenesis), which only becomes evident after several days of UV application.

To better understand MED and MMD, it should be said that both are individual values. The lowest effective dose developing a sunburn as well as the value producing a suntan depend distinctly on the skin sensitivity of the person.

In order to eliminate these individually influencing factors, MED and MMD have been standardized. With standardized MED and standardized MMD values, sunlamp products can be characterized and specified and become comparable with respect to their biological capabilities. Such information based on these standard values are of higher ranking meaning than are statements about the physical data such as UVB/UVA ratio or UVB percentage.

Comparing Standard MED And MMD

By comparing MED and MMD values of tanning units, it may be surprising that the required exposure time for reaching 1 MMD is usually longer than the corresponding time for reaching 1 MED. This seems to indicate that it is impossible to tan without first developing skin redness. At the same time, the question comes up: How can we achieve tanning slowly, progressively, and safely without producing a sunburn?

To shed some light on this question, consider the following: MED and MMD are standardized values and valid for unprotected and untanned Skin Type II. This means that such given values are basically only valid before undergoing the first exposure.