Suggest Remedy For Painful Blisters On Hand Leaving A Bruise Upon Popping

my husband has been getting blisters on the backs of his hands for 3 years now. they go away and keep coming back and are getting bigger and some are forming into a cluster. after they go down or bust they leave a bruise where they had been. He has been to a dermatolagist and they have no clue what they are. He was playing with one of our dogs and one of her teeth broke the skin and he has had these ever since. The ones he has now are painful. could you please help us in figuring out this problem. I have taken some pictures of his hands and will be glad to send them to you. My email address is YYYY@YYYY . Thank you so much for your time.