Human Flea Allergy Dog Allergies, My Shihtzu Keeps Scratching And Scratching, Ideas ?

Dog allergies, my shihtzu keeps scratching and scratching, ideas ? - human flea allergy

I have a shihtzu man, aged 3 years and I knew he was itching for a response to a change of diet or start, but it now seems to be itching all the time. What can I do? I have a shower and ready for him, once a month and I can not wait to eat the same food. If you are like human allergies, could be anything! I do not know where to start. ? It is not fleas! He has a sensitive skin.