Higher Histamine Sensitivity in Non-atopic Subjects by Skin Prick Test May Result in Misdiagnosis of Eggplant Allergy

Eggplant (aubergine; Solanum melongena L.), a member of the nightshade family, is widely consumed as a vegetable. A high incidence of allergic reactions to eggplant appears to be commonly experienced among Indians, presumably due to its high histamine content. Therefore, it appeared interesting to investigate the histamine content of different varieties of eggplant (green and purple round; green and purple slender long) using raw, cooked, and dialyzed extracts. A significant varietal difference in the histamine content of eggplant varieties was observed. Highest amount was present in the green round variety (2.41 mg/100 g fresh weight in raw and 2.07 mg/100 g in cooked extracts). The histamine content of other varieties (in mg/100 g raw) is: green slender long (1.80), purple slender long (1.35), and purple round (0.89). Histamine is stable to heat-processing, since only 11-14% loss was observed upon cooking. Skin prick test (SPT) on non-atopic subjects (without any history of eggplant allergy) using four varieties of raw and cooked eggplant extracts revealed that only subjects with a lower threshold for histamine produce positive results equivalent to that seen between 10-100 g/mL histamine dihydrochloride. It can be concluded that the amount of histamine present in eggplant does not produce a positive SPT response in a majority of non-atopic subjects, and that a positive response in a few subjects are likely to be misdiagnosed as eggplant allergy.