as a kid (about 10yo it started) i started getting hives, mum hadnt changed anything at home, nor had i started eating new or different foods, after some time testing different things it turned out to be citrus that caused it. was getting them on a friday after sports day when they served out oranges

i can have lemon but all other citrus is out unless i want hives the size of 50c pieces

apparently its a common cause