Minimal Erythema Dose (MED) Testing

Summary

This article describes how to conduct minimal erythema dose (MED) testing in order to determine the lowest dose of ultraviolet radiation that will cause erythema (burning) when administered to an individual.

Abstract

Ultraviolet radiation (UV) therapy is sometimes used as a treatment for various common skin conditions, including psoriasis, acne, and eczema. The dosage of UV light is prescribed according to an individual's skin sensitivity. Thus, to establish the proper dosage of UV light to administer to a patient, the patient is sometimes screened to determine a minimal erythema dose (MED), which is the amount of UV radiation that will produce minimal erythema (sunburn or redness caused by engorgement of capillaries) of an individual's skin within a few hours following exposure. This article describes how to conduct minimal erythema dose (MED) testing. There is currently no easy way to determine an appropriate UV dose for clinical or research purposes without conducting formal MED testing, requiring observation hours after testing, or informal trial and error testing with the risks of under- or over-dosing. However, some alternative methods are discussed.

Protocol

1. Preparing for UV Exposure

1. Explain to the participant how MED testing works ("I'm going to expose some skin on your arm to UV light over the course of about 20 min, and tomorrow, we're going to check that section of your skin in order to determine how sensitive you are to the light. You may experience a sunburn in the small areas that we expose to UV. If the sunburn is painful or bothers you, you can treat it like you would any other sunburn.")
2. Staff and participant should wear UV protective glasses.
3. The participant should be wearing a short-sleeved shirt or roll her sleeve up.
4. Have the participant put o....

Results

Figure 1. The four steps of conducting MED testing: preparing for UV exposure, conducting UV exposure, assessing the MED, and determining the MED.

Discussion

Ultraviolet radiation (UV) therapy is sometimes used as a treatment for various common skin conditions, including psoriasis, acne, and eczema. The dosage of UV light is prescribed according to an individual's skin sensitivity, which is determined as a function of the individual's Fitzpatrick skin type I through VI (very fair to very dark).² Human skin varies in its sensitivity to UV radiation because of varying degrees of skin pigmentation, thickness, and other factors. Thus, to establish the proper dosage of .......