May be you can check if there are rashes underneath or even flip the ears to chk for infection. Sometimes they love to rub their ears and can cause hair loss. If it is allergy, then should find hair losing in a few places where there is skin rash I would think. Usually hair loss is associated with skin infection in which case you should consult the vet on the rashes, eg. becoming botak with bumps or fungus growing. Otherwise it may just be the normal shedding.
Fungus are of course more serious than ocassional bumps which may be dark red, purple or even black in colour. If you bring it to the vet they will probably recommed some sensitive skin shampoo for your dog and add some antibiotic medicine and prescribe another antibiotic solution for you to apply onto your dog which will cause $$$. The truth of the matter is that it is oh-so-common for dogs to get skin problems from time to time and it will often go away with time. I have used these expensive medicines and did not see much improvement (be it diet, creams, shampoo and what-not). MY dog had amongst other mild skin rashes from time to time, fungus patch of 2-inch diameter with slight inflammation and in the end I gave up on the medicine and applied my calamine lotion on the spot and voila! It dried up in days and my dog loves the soothing cool feeling of calamine lotion than the antibiotic solution which smarts terribly.
Having said that if the fungus starts spreading to many patches of the body then your dog may have contracted mange/dermatitis and is advised to be put on medication for a while.
In other words I think you need to play by ear on whether it is a temporary skin allergy or serious skin disease. If you keep referring to the vet on every skin rash it would cause a big hole in your pocket!