Instead, they believe they're allergic to the fish they've consumed.
It was this that convinced me tuna was the culprit.Amena Warner, national nurse advisor for Allergy UK, says: 'If a fish isn't frozen or iced quickly enough after it is caught, bacteria quickly build up inside it, which can create the scombroid toxin.This then converts the amino acid histidine, which occurs naturally in the fish, into histamine.'According to Dr Gnanakumaran, although everyone who eats affected fish may be struck down by scombroid poisoning, those sensitive to histamine (ie, those who already suffer from allergies) will be more prone to it.'The differences are subtle but a true allergic reaction will trigger tingling or swelling of the lips or tongue as soon as the food touches them, followed by throat constriction and an itchy rash,' explains Dr Gnanakumaran.Other symptoms can include a severe headache, a sudden drop in blood pressure that leaves you feeling faint, a racing heart, tight chest and shortness of breath, as well as sickness and diarrhoea.'Although allergies can develop at any time in our lives, in the majority of cases when someone without a previous fish allergy suffers a reaction after eating tuna, it will most likely be as a result of scombroid poisoning.'According to Food Standards Agency recommendations, pregnant or breastfeeding women should not eat more than two medium tins of tuna or one fresh tuna steak a week because it is high in mercury, which can be passed through the umbilical cord or breast milk, potentially damaging the nervous system of a foetus or baby.'Unfortunately, studies have proved that the scombroid toxin is resistant to smoking, cooking, canning and freezing.So if the toxin is already there before the fish is dispatched for human consumption, it is there for good,' says nurse Amena Warner.'Neither can its presence be detected by appearance or smell.