I’m here to tell you as a Pediatrician to stop living like you’re in the 1940’s and to stop using Benadryl for everything related to allergies or allergic reactions.
Antihistamines work by counteracting histamine throughout the body.
Benadryl is an older, 1st generation antihistamine. First generation antihistamines are not very selective, so they can affect other pathways in the body that can lead to side effects to include drowsiness, hyperactivity in 10 to 15% of kids, agitation, hallucinations, and rarely, but still possibly, seizures and death.
Newer, or 2nd generation antihistamines like Zyrtec, Claritin, Allegra, and Xyzal have similar onset of action, last longer, and have less side effects (most notably less sedation) because they are more selective for histamine receptors.
Especially in scenarios where you’re concerned about anaphylactic reactions, for example to insect bites or foods, you don’t want to cloud the picture by giving a child a medication that may induce drowsiness leading to an inappropriate diagnosis of anaphylaxis.
In summary, Please, please, please stop using Benadryl for all things related to allergies and allergic reactions. There are better options that don’t lead to concerning side effects. Epinephrine is the only validated treatment for anaphylactic reactions!