well if it is the summer or around summer the answer is shedding
I would definitely talk to the vet. You don't know what it is so it could potentially be really bad.
fleas
Your dog most likely has ringworm. Sorry.
If a dog (any dog) is losing hair in big enough patches to see his bare skin where he has lost it, he probably has mange, and should be seen by a vet. There are other causes too,but mange is the first thing the vet will suspect. Take him to the vet.
First of all don't let your dog play with a sick dog. Tell the owner of the sick dog to take it into a Veterinarian. If your dog is losing large amounts of hair or has bald spots on his coat, take him into your Veterinarian to be checked out for such things as demodex or sarcoptic mange mites or other issues. Losing small amounts of hair is normal as they are shedding. Make sure you have your dog on a good brand name of dog food.
Is you dog showing signs of a pot belly or eating more than usual? Losing hair is a sign of cushings disease
I used Epi-Smoothe on my dog. She has some spots where her fur is falling out
You should trim your dog's hair because there could be a lot of trapped dirt or fleas in there. You should also do it to make your dog look nice.
If you own a dog with long hair then you should use a brush with long bristles or if you have a dog with short hair then you should use short bristle brushes to brush them.
Look up Mange... and consult a Veterinarian.
There are many reasons that your dog is having diarrhea and losing hair. Take your dog into your Veterinarian to have a check up. Bring in a small sample of your pet's feces too so the Vet can check it for internal parasites or signs of blood. Don't try to diagnose your dog yourself, take to your Vet. Make sure you are feeding your dog a good name dog food and not some cheap store brand food.
Your dog probably has allergy's and is gnawing on his feet to try to stop the itch or your dog is getting old and has callus from so much use.
only if its hair is getting to long