The impact of ultraviolet exposure on patch testing in clinical practice: a case-control study

Current guidelines suggest waiting a full 6 weeks between ultraviolet (UV) exposure and patch testing owing to the localized and generalized cutaneous immunosuppression it induces, yet there is a dearth of evidence as to the duration of this immunosuppression.

To determine whether there are any significant differences in the rates of positive patch-test reactions between patients who had received a significant exposure to UV within the previous 6 weeks, and similar patients who had not received such an exposure.

Rates of positive patch-test reactions were compared between patients undergoing patch testing for generalized eczema who had completed a course of phototherapy within the preceding 6 weeks, and matched controls who had not. Patients were matched for sex, age and naivety to systemic therapy.

Of the 22 patients who had received phototherapy, 7 exhibited at least 1 positive reaction, compared with 6 of the 22 controls; this result was not significant (P > 0.05).

The cutaneous immunosuppression induced by UV exposure appears to be fully resolved within < 6 weeks. This suggests it may therefore not be necessary in all cases to wait the full 6 weeks following significant UV exposure before undertaking patch testing.