How much time does it take for anaphylaxis to kick in after a reaction?

Anaphylaxis: Anaphylaxis can occur from seconds up to approximately 6 hrs after an allergic exposure ( food, sting, medication , etc).

Anaphylaxis onset: Almost always within minutes. So fast that if one is at risk of a repeat event of anaphylaxis, an automatic injector of epinephrine should be carried at all times. Fatalities occurred from delaying treatment with epinephrine. However, a new form of delayed anaphylaxis from reactions to 'red meat' has been discovered. Happens in those with frequent tick bites. I've seen several. Get an allergist.