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Juvenile xanthogranuloma (JXG) is one of the most common forms of non-Langerhans cell histiocytosis in children. Although it usually presents as a self-limited skin lesion with typical histopathology, JXG can be challenging to diagnose due to an atypical initial presentation with corresponding variable histopathology for different stages of development. We present challenging cases of JXG from Sydney Children's Hospital, collected over 10 years - two with multisystem involvement and concomitant urticaria, one associated with neurofibromatosis, and one case of giant JXG with an initial histopathological challenge. Although JXG has been reported with urticaria pigmentosa, in two of our cases persistent urticaria, in association with JXG is discussed., (© 2011 The Authors; Australasian Journal of Dermatology © 2011 The Australasian College of Dermatologists.)

Cutaneous immunity, which is a key defence against the development of skin cancers, is suppressed by even small doses of ultraviolet (UV) radiation. Preventing this UV-induced immunosuppression may therefore reduce the incidence of skin cancer. Nicotinamide (vitamin B3) has immune-protective and cancer-preventive effects against UV radiation in mice, and we have shown previously that topical nicotinamide is immune protective in humans. Using the Mantoux model of skin immunity in healthy volunteers, we compared oral nicotinamide to placebo (both administered for 1 week) in a randomized, double-blinded, crossover design against the effects of solar-simulated ultraviolet (ssUV) radiation on delayed-type hypersensitivity to tuberculin purified protein derivative. Discrete areas of the back were irradiated with low doses of ssUV daily for three consecutive days. Immunosuppression, calculated as the difference in Mantoux-induced erythema of irradiated sites compared with unirradiated control sites, was determined in volunteers taking oral nicotinamide and placebo. Significant immunosuppression occurred in an UV dose-dependent manner in the presence of placebo. Oral nicotinamide, at doses of either 1500 or 500 mg daily, was well tolerated and significantly reduced UV immunosuppression with no immune effects in unirradiated skin. Oral nicotinamide is safe and inexpensive and looks promising as a chemopreventive supplement for reducing the immunosuppressive effects of sunlight.