Dogs like humans suffer from dust allergies or an allergy to pollen. The condition as in humans is often hereditary and they can have a reaction to grasses, mould or pollen. However dogs do not exhibit the same reaction as humans they tend not to sneeze, but the condition of their coat suffers.
If your dog has begun to scratch, bite, or lick himself then he may well be suffering from hay fever.
When dogs do this constantly, the action of the tongue can create secondary problems, such as infections or even other sores. The treatment varies depending upon how serious the condition is. Some dogs respond to a medicated shampoo.
When the condition is more serious then the veterinarian can do an allergy test to pinpoint exactly what the dog is showing an allergic reaction towards. Oral cortisone or antihistamines can help to bring the scratching under control. Your dog can have injections prior to Spring to increase his tolerance to whatever is giving him an allergic reaction.