Med

The erythema threshold of ultraviolet light, or UV radiation, is the weakest, but still (usually sharply) distinguishable skin redness from the non-irradiated environment, which can be read 7 or 24 hours after the test irradiation.

First described by von Wucherpfennig in 1931.

Light dermatoses or in the case of UV-provocable dermatoses(persistent light reaction, photoallergic eczema or phototoxic dermatitis, light urticaria, lupus erythematosus, protoporphyria erythropoetica, Hidroa vacciniformia, polymorphic light dermatosis etc.) by a possibly reduced MED-UVB or MED-UVA. See also photo patch test and photo provocation test.

In accordance with the exponential progression of the UV reaction on the skin, a series of previously non-UV exposed test fields (5-8 small areas on the buttocks or back) are exposed to geometrically or arithmetically increasing irradiation times or energy quantities to determine the MED-UVB and MED-UVA and read and evaluated according to the above definition. Information on normal values or reference ranges for MEDs must always be seen strictly in the context of the methods used; in particular, the irradiation spectra used are of crucial importance. A comparability of MEDs based on different irradiation sources can be achieved by conversion to the standard erythema dose (SED).

1. Gambichler et al (2006) Reference limits for erythema-effective UV doses. Photochemical photobiol 82: 1097-1102
2. Wucherpfennig V (1931) Biology and practical applicability of the erythema threshold of UV. Radiotherapy 40: 201-243