Lisheid,
You certainly can use benadryl safely in your cat. However, if the irritation gets worse or does not respond to the benadryl within 72 hours, you should have the area looked at by a vet. Cats get a number of different skin disorders, not all of which are allergic in nature.
I hope this helps,
Dr. Karen
Cat Veterinarian
20+ years experience as a veterinarian and cat owner.
You are very welcome.