Vegans and vegetarians often consume foods containing
photosensitizers capable of triggering phytophotodermatitis. The potential effect of vegan and
vegetarian diets on the response of psoriatic patients undergoing
phototherapy is not well characterized. We assessed clinical outcomes of vegan, vegetarian and omnivore adult psoriatic patients undergoing band ultraviolet B
phototherapy (NB-UVB). In this multicenter prospective observational study, we enrolled 119 adult, psoriatic patients, of whom 40 were omnivores, 41 were vegetarians and 38 were vegans, with
phototherapy indication. After determining the minimum erythemal dose (MED), we performed NB-UVB sessions for 8 weeks. The first irradiation dosage was 70.00% of the MED, then increased by 20.00% (no
erythema) or by 10.00% (presence of
erythema) until a maximum single dose of 3 J/cm2 was reached and constantly maintained. All the enrolled patients completed the 8 weeks of
therapy. Severe
erythema was present in 16 (42.11%) vegans, 7 (17.07%) vegetarians and 4 (10.00%) omnivores (p < 0.01). MED was lowest among vegans (21.18 ± 4.85 J/m2), followed by vegetarians (28.90 ± 6.66 J/m2) and omnivores (33.63 ± 4.53 J/m2, p < 0.01). Patients with severe
erythema were more likely to have a high furocumarin intake (OR 5.67, 95% CI 3.74-8.61, p < 0.01). Vegans consumed the highest amount of furocumarin-rich foods. A model examining
erythema, adjusted for gender, age, skin type, MED,
phototherapy type, number of
phototherapies and furocumarin intake, confirmed that vegans had a lower number of treatments. Vegans had more frequent severe
erythema from NB-UVB, even after adjustment of the
phototherapy protocol for their lower MED. Assessing diet information and adapting the protocol for vegan patients may be prudent.