But deaths have occurred in people who had only mild attacks before. The answer is to be prepared . When the same protein or drug reaches the IgE on the cells, these substances are released, causing blood vessels to relax, which makes them leaky and can cause swellings and a fall in blood pressure. At the same time they can make the breathing passages become narrow. Histamine is one of these substances released from the cells.
Antihistamines are medicines which stop histamine from working.
So you might think that they would be good for nut allergy, and so they can be when the reaction is mild. But as tablets they take about an hour to get into the bloodstream properly, and this is far too slow to save lives in serious reactions. Antihistamines also don't prevent all the effects of histamine, for example effects of histamine on the heart, in serious reactions. Older antihistamines made people drowsy, which is dangerous if you have to drive. So it could add to your danger if you take one and then drive to get medical help.