This article is from the Children Allergies and Asthma FAQ, by Eileen Kupstas Soo email@example.com with numerous contributions by others.
Immediately. The speed of your reaction depends on your body, whether
you are able to get a dose of epenephrine immediately, how much of
the allergen is absorbed, and a few other variables and is therefore
unpredictable. The safest thing to do is to get medical attention as
quickly as possible.