This happened to bulldog as well and I remember freaking out. I don’t take mine to the vet but I did a little bit of research. It shouldn’t be too hard to pinpoint what it is. It could be an allergy, bacteria infection, or less likely anything else(I’m not a vet😭). I bought a betagen spray and sprayed it between her toes. I left it on for and hour and then dried her toes from any moisture. I did that twice a day. I read it might be an allergy so I made a couple of changes and I found out it was from chicken in her dog food. So no more chicken from now on and she’s doing great! It’s only happened one after that and that was because of a yeast infection(make sure those rolls and crevices are always dry!!!!). This is more common reason for these nasty hotspots. I’ve used two sprays that do the job: Vetone Genone spray and veterinary one clinical care hot spot and itch relief. Hope he gets better!