Background: Heroin and its contaminants may be an important source of allergens in young people. We present a case of severe endophthalmitis in a patient that also suffered from anaphylactoid symptoms (hypotension, urticaria, glottic oedema) whenever he ingested lemon. Methods: Prick tests with a battery of 42 aeroallergens including fruits and citrus fruits (orange, mandarin, grapefruit and lemon) and specific IgE to these allergens were carried out. Immunodetection was performed using the patient's serum and the following allergens: lemon, Candida, Aspergillus, Penicillium and Alternaria recombinant Alt 1 (Laboratories Diater). Results: Skin tests were negative for Candida, Penicillium, Aspergillus and Cladosporium (ALK-Spain) as were specific IgE antibodies for CAP (Thermofisher, Sweden) and positive only for lemon and, doubtfully, to Candida. Specific IgE tests to pollen, arthropods, fungi, dander and foods were positive only for lemon (0.49 kU/L). Serological study of fungi ruled out fungal infection at that time. The immunodetection showed that the patient's serum recognised a protein of approximately 25 kDa of lemon peel, one of approximately 12-13 kDa of Penicillium, and perfectly recognised Alt a 1. Conclusions: Lemon surface can be contaminated by Candida and other fungi. In heroin addicts with positive skin tests for lemon, the possibility of these serious complications should be taken into account. (C) 2016 SEICAP. Published by Elsevier Espana, S.L.U. All rights reserved.