Objective evaluation of sunscreen in a patient with solar urticaria

Abstract Sunscreens are an important part of photoprotection for patients with photodermatoses, such as solar urticaria (SU). Despite long ultraviolet (UV)A and visible wavelength photosensitivity in many patients with SU, sunscreens can still be beneficial (Beattie PE, Dawe RS, Ibbotson SH, Ferguson J. Characteristics and prognosis of idiopathic solar urticaria: a cohort of 87 cases. Arch Dermatol 2003; 139:1149–54). However, unlike the objective assessment of photosensitivity by monochromator phototesting, formal evaluation of sunscreens’ effects is more challenging. We report a 32-year-old man with a 2-year history of immediate-onset photosensitivity, confirmed as SU on monochromator phototesting, with an action spectrum of UVB, UVA and visible light (305–460 nm). He had been using Nivea Sun SPF (sun protection factor) 50+ (Beiersdorf) and reported that this increased his tolerance of natural light from 10 to 60 min. Based on the sunscreen constituents, we were surprised to hear that it was so effective as there was no mineral constituent. Therefore, we evaluated his SU photosensitivity by UVA testing using a metal halide source [Honle UVASPOT 400 T; 24.09 mW cm−2; minimal urticaria dose (MUD) < 0.13 J cm−2] through his own sunscreen and, for comparison, Dundee Cream Beige (Tayside Pharmaceuticals) and LaRoche Posay Mineral One shade 01 (L’Oreal), both of which contain reflectant titanium dioxide. Three areas, measuring 15 × 10 cm, were marked out on his back and 0.15 mL of one sunscreen was applied to each. Each area was then irradiated through a Daavlin template using multiples (1×10) of the MUD and sites were observed for 30 min. As he was so severely photosensitive, none of the sunscreens affected the threshold MUD, but we noted delay in the induction of SU. Dundee Cream Beige offered minimal photoprotection, with urticaria occurring at 10 min vs. 5 min without sunscreen at 1 × MUD. LaRoche Posay SPF delayed the onset of SU to 30 min, and the reaction was less intense at 1 × MUD. However, the most marked effect was with his own Nivea SPF 50+. Urticaria induction was delayed to 30 min at 1 × MUD and was less intense, but it was also delayed to 15 min and less intense at a dose of 4 × MUD, confirming his impression that this sunscreen was of clinical benefit. We highlight this case to show how photodiagnostic testing can be employed to evaluate objectively the sunscreen effects in patients with photosensitivity. Conventionally, it is assumed that titanium dioxide-based products, such as the Dundee creams, are required in patients with longer UVA/visible light sensitivity, but with refinements in the development of new sunscreen products, this may not necessarily be the case.