Brazil nuts are the second most frequent cause of nut allergy in the UK, and one poor woman has become the case study in the first ever incidence of sexually transmitted allergic reaction. After intercourse with her boyfriend, who had earlier consumed Brazil nuts, she developed urticaria and mild dyspnea. Skin prick testing with a sample of his semen produced reactive results, compared with a sample of his semen before nut consumption, which was negative. The pair were in a committed relationship, and he, being aware of her severe allergy, had bathed, brushed his teeth and cleaned his nails immediately before intercourse. He had consumed 4-5 Brazil nuts between two and three hours earlier. Her symptoms included itching and swelling of her vagina and vulva, and faintness. After taking 10 mg of cetirizine, she started to improve within 45 minutes. The woman had been confirmed as nut allergic 2 years previously, but had had reactions before, the most severe being at age 6. She was advised to avoid all nuts because of negative reactions to peanuts, walnuts, almonds and hazelnuts, and had done so. Initially there was confusion about the cause of this outbreak, but after the skin prick tests it became clear that the Brazil nut proteins had been secreted into his semen after her partner had eaten them. The researchers, from the Department of Immunology, St Helier Hospital, Carshalton, UK, acknowledge that this is the first instance that they are aware of with evidence to support a sexually transmitted reaction – although one woman suffered anaphylaxis when her partner kissed her after consuming shellfish. Source: Journal of Investigational Allergology and Clinical Immunology First published in 2007 Click here for more research reports Top of page