How do you get a dog to grow its hair back?

Your dog's hair should grow back naturally though depending on the cause of the scratching and hair loss it might not be as thick as it was.

I'd suggest the cause of the scratching/hair loss be looked in to and trated to make sure there is no repeat so your dog's health does not suffer.

Hair loss in dogs can be caused by many things - such as Allergies, fleas or mites which can trigger your dog to scratch the affected area in an attempt to bring relief. his in turn can cause dog hair loss.

If in doubt - see your vet.

They usually tend to scratch due to stress, allergies, or things like that. Yea see your vet. They'll prescribe something for you.