When you have a food allergy, your reaction can start within minutes of eating the trigger food. In some cases, it might take up to 2 hours.
The length of the reaction depends on the severity of your allergy, the amount you ate, and how quickly your body responds to treatment.
Mild allergic reactions — like itching, hives, or stomach discomfort — usually last a few hours. If your symptoms stay mild and go away with antihistamines, you’ll likely feel better by the end of the day.
However, every person reacts differently. You may notice lingering effects, like fatigue or skin irritation, for 1 to 2 days afterward.
More serious reactions, like anaphylaxis, require immediate medical attention. If you experience throat swelling or difficulty breathing, use an epinephrine auto-injector (EpiPen) and call emergency services.
Even if you feel better after using epinephrine, the reaction can return. This second wave, called a biphasic reaction, can happen hours later — sometimes up to 12 hours after the initial onset of symptoms.
That’s why it’s important to seek medical attention. Take action at the first sign of symptoms and avoid waiting to see if the reaction gets worse.