 [ Symptoms ] i was bitten by a spider on the inside of my forearm and now it is very swollen red and painful will benadryl help [ Disease ] unfortunately spider bites have a tendency to cause infection and i believe we may be at this point in this situation this could be the start of cellulitis which is a bad skin infection i would advise seeing a health care provider as soon as possible an antihistamine like benadryl will not help