Real-life experience from a tertiary phototherapy center on solar urticaria: clinical features, management, and long-term outcomes from a twenty-year cohort

Background: Solar urticaria (SU) is a rare, chronic photodermatosis characterized by immediate whealing upon exposure to ultraviolet (UV) or visible light. Tolerance-induction phototherapy (photohardening), delivered as action-spectrum desensitization or cross-spectrum photohardening, represents the mainstay of management in antihistamine-refractory cases, yet data on its long-term real-world efficacy and safety remain limited. The aim of the study was to evaluate the clinical and photobiological characteristics, therapeutic outcomes, and long-term efficacy of tolerance-induction phototherapy in patients with SU managed at a tertiary phototherapy center. Methods: A retrospective observational study was conducted on 53 patients with phototest-confirmed SU treated with UVA or narrowband UVB (NB-UVB) phototherapy between January 2005 and June 2025. Treatment regimens were tailored to individual action spectra and, in selected cases, applied as cross-spectrum photohardening according to clinical practice and safety considerations. Clinical responses, phototolerance (minimal urticarial dose, MUD), and adverse events were recorded. Long-term outcomes, including remission persistence, relapse, and patient satisfaction, were assessed through complete follow-up (median 4.7 years). Results: At the end of therapy, 33 patients (62%) achieved complete remission, 15 (28%) partial improvement, and 5 (9%) showed no change; overall, 91% experienced at least partial benefit. Remission was maintained in 31 patients (58%), while 22 (42%) relapsed after a mean of 4.2±1.6 years. In patients with available post-treatment phototesting, those maintaining remission exhibited a mean fourfold increase in phototolerance. The mean satisfaction score was 8.8±0.7 (median 9). Only mild transient erythema (15%) and pruritus (7%) were reported, with no serious adverse events. Conclusions: Tolerance-induction phototherapy with UVA or NB-UVB is a safe and highly effective first-line treatment for solar urticaria, providing durable phototolerance and long-term remission in most patients. The extended follow-up confirms its sustained efficacy and favorable safety profile in real-world clinical practice.