Chicharro et al. review the results of induction of light tolerance in patients with solar urticaria (SU). The mechanism by which tolerance is induced by UV radiation or visible light remains partially unknown. Patients with severe SU are rarely able to get enough exposure to acquire good tolerance. In moderate cases, however, repeated exposure to natural light can have a natural hardening effect and rarely gives rise to lesions on areas such as the face and the back of the hands. The proposed mechanisms include the saturation of IgE antigen-binding regions, the alteration of chromophores in the skin, and UV-induced immunosuppression (mast cell depletion or degranulation). The thickening and/or pigmentation of the epidermis can also contribute to this natural hardening. This phenomenon can be used to treat SU with incremental exposure to artificial light sources. Various treatment alternatives exist:

Systemic psoralen–UV-A (PUVA)1: This treatment has yielded satisfactory results but is not the first-line option due to its stronger association with photocarcinogenesis.

Hardening with the triggering light source: This treatment can require long-term maintenance and the effects only last a few days.

Inhibition spectrum treatment: In this treatment modality, the therapeutic spectrum is different from that which triggered the condition (narrowband UV-B radiation could be used in SU induced by UV-A and/or visible light). This modality, previously reported by other authors,2,3 is the one described by Chicharro et al. in the present issue. This is the second case series, after that of Calzavara-Pinton et al.,3 to describe the use of narrowband UV-B to treat patients with SU.