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Updated: Aug 11, 2026
Minimal Erythema Dose (MED) Testing
Published on: May 28, 2013
[The prospective multicenter study on standard photopatch tests by the French Society of Photodermatology from
F Leonard1, H Adamski, A Bonnevalle
1Service Dermatologie, Hôpital Robert Debré, Reims.
Introduction:
To develop a standard panel of photopatch tests, the French Society of Photodermatology conducted a prospective study from 1991 to 2001 on the frequency of photoallergens encountered in France and on the relevance of the choice of the various photoallergens.
Patients And Methods:
Thirteen photobiology centers participated in the study from 1991 to 1995, and ten centers from 1995 to 2001. A set of 3 samples of photopatch tests was applied on any patient suspected of photoallergy. On Day 2, two sets were irradiated with ultraviolet A (UVA) and total spectrum (DEM 0.75); with the third set being used as control. Readings were made on D3 and D4.
Results:
Two thousand sixty-seven patients were tested. Eight hundred fifty-six, i.e., 41% exhibited one or several positive tests. In the majority of cases it was a photoallergy (39.7 to 60% of cases) and eczema (29.5 to 45.6%). Photoaggravation was infrequent (7.9 to 10.3%). Cases of phototoxicity were rare. Sesquiterpenic lactones constantly provoked photoallergy, with 12 cases in 10 years. Although phenothiazines were the most photosensitizing allergens up until 1995, they were then overridden by ketoprofen in 1996 with 107 cases of UVA photosensitive reactions (75 cases) and total spectrum (32 cases). These were followed closely by sun screens, benzophenone (notably Eusolex 4360 with 54 pertinent cases of photoallergy) and dibenzoylmethane (with 31 cases due to Eusolex 8020). UVB filters were all potentially photosensitizing but to a lesser degree from 1 to 5 cases).
Discussion:
Our results differ from those of Anglo-Saxon teams in the appearance of a new photoallergen, ketoprofen, which provoked numerous photosensitivities in both UVA and UVB. This justifies the systematic addition of this substance in our prospective set. Photoallergy was relatively rare, with around 100 cases reported within 10 years. Total spectrum irradiation of the photopatch tests revealed photoallergies that would not have been found with UVA alone.
Conclusion:
Study of photopatch tests has permitted the uniformization of the methodology in France, an overview of the frequency of the photoallergens tested and the development of a new standard set.
