Thirty hours evaluation of UVB induced erythema by chromometry and microflowmetry

BACKGROUND: Individual UVB photosensitivity is usually investigated by determining the minimal erythemal dose (MED). Nevertheless, factors such as room light intensity and subjective experience of the observer can influence the erythema perception and, therefore, the MED assessment. OBJECTIVE: To evaluate the relationship between the clinical and the chromometric and microflowmetric analyses of the UVB-induced erythema in 2 healthy volunteers. METHODS: A bank of 6 fluorescent mercury vapor tubes (Philips TL 12/20 W) was utilized as a source of UVB light. Three skin areas (4 cm2), from the dorsal region of each subject, were irradiated with 3 different UVB doses corresponding to: (1) MED; (2) 0.7 MED, and (3) 1.3 MED. RESULTS: (1) both microflowmetric and chromometric parameters reached a maximum peak 10-12 h after irradiation and maintained high values also 30 h after irradiation; (2) both microflowmetric and chromometric values were directly related to the UVB doses; (3) in some cases the microflowmetric values started to increase when the chromatic changes were still undetectable. CONCLUSION: These preliminary data confirm that the visual determination of MED performed 24 h after irradiation is a correct procedure. Nevertheless, the microflowmetric may precede the chromatic changes suggesting that vasodilatation follows irradiation without a latent period.