How do you know if it’s an allergic reaction?

What the evidence says

Most allergic reactions are mild to moderate. Look for skin symptoms like hives, itching, redness, or swelling of lips or face, a tingly mouth, sneezing, a runny or itchy nose, or mild stomach upset. These usually start within minutes and can be treated with an antihistamine.

A severe reaction, called anaphylaxis, is different and dangerous. Watch for coughing, wheezing, shortness of breath, chest tightness, a hoarse voice or trouble swallowing, along with signs of low blood pressure like feeling faint, dizzy, or passing out. In babies, this can look like sudden paleness and floppiness.

Timing can vary: symptoms usually appear within minutes to two hours of exposure, though rarely they can take longer, and some reactions have a second wave hours later even after treatment. If your child has known allergies, your allergist can give you an action plan describing exactly what counts as mild versus severe for them. If you ever see breathing difficulty, throat swelling, or fainting, this is anaphylaxis: use an epinephrine auto-injector if prescribed and call 911 right away, since anaphylaxis can worsen quickly and is life-threatening without prompt treatment.