Carlos said
They both stop itching, but when do I use one over the other?

itsme_ulan said
They are actually both antihistimines (although Benadryl does come in a topical formula).Allegra requires a prescription, Benadryl does not. Allegra has a formulation that lasts 24 hours (the 180mg version); their other formulation (the 60mg version) lasts 12 hours. I believe Benadryl allergy is a 50mg version (so you need to take a more doses per day for the same length relief).The active ingredient in each is different as well: Allegra 180mg (the 24 hour extended version) has two active ingredients (fexofenadine hydrochloride and pseudoephedrine hydrochloride); regular Allegra's active ingredient is fexofenadine hydrochloride, and Benadryl's active ingredient is Diphenhydramine.If both work equally well for you, it's probably more economical for you to go with the prescription (if you have health insurance) - the co-pay will be less for a 30 day supply than it would cost for 30 days worth of Over The Counter Benadryl.

arii_lins said
Allegra is an antihistamine; I believe it's taken internally, and it will address some of the symptoms of an airborne allergy--runny nose, itchy eyes, achy muscles, etc.Benadryl is a topical anti-itch (and mildly anesthetic?) goo to reduce the itchiness of a bug bite or rash or whatever. Not the same category as Allegra; it's more like calamine lotion (white stuff often used for poison ivy/oak).