This form of efflorescence is common in horses and is often associated with food allergy or insect allergens. On the other hand, exercise-induced urticaria has also been described in horses and humans. However, research into the cause of urticaria is usually very laborious and time-consuming.
As there is no allergen-free grain, a horse with urticaria must not be fed concentrated feed and should be put on shavings and follow a strict hay/grass diet, i.e. no muesli and no treats for at least 2 months. Even after that, at least treats and muesli should be avoided, and if they are fed, then only from one type of grain. It is also very helpful to keep a diary where any kind of changes or abnormalities can be documented and thus traced.