Bichons are prone to hot spots, as well. VERY frustrating, it takes trial and error to find the trigger. It usually is an allergic reaction.

You can treat the spot with Gold Bond Medicated powder, start the MOMENT you see something odd and apply 3 times daily. This just helps the symptom.

The cause could be food related, or environmental. Or even a reaction to a flea bite. The fact that it is always in the same spot suggests an allergy.

Think about what food and treats you use. Be consistent in what you give for a week or 2, then change ONE THING.

For bichons, we mostly use grain free foods, as the grains are a high trigger. I have 2 which are highly susceptible, so I must use grain free treats for them, as well.

Chicken is a high allergen, as is fish.

If it is environmental, it will depend where your dog goes outside. Maybe you visit a dog park once a week, and it is something there. Or maybe you both visit a friend on th weekends.

I found keeping a journal helped (lots of bichon folks must) as you WILL forget which day you gave the dog which food, or went to visit which place.

Good luck!