An
allergy to some type of
pollen. This mostly shows up in
spring, since that's when most of the
flowers appear. Hay fever is usually specific to a few species of flower (the flowers of the
olive tree are a common cause in
Israel).
To test which flower it is you're allergic to, they put a small grid on your skin, and scratch each square with stuff from a different plant. The one that shows red is the one you're allergic to. It is wise for the medical staff to have some anti histamine handy while doing this.