Get Your Dog Care Questions Answered by Experts
If he seems to be itching or scratching a lot, some benadryl might help. The dosage that my vet recommends is 1 mg per lb of body weight given every 8-12 hours.
If you don't see this resolve, you will want to see your vet. This might be something more than an allergy.
Let me know if you still have questions.
It would be impossible for me to tell you without being able to see it.
If you suspect that this is just an abrasion, you can wash the area well with peroxide and then apply some neosporin ointment.