This is quite common in bichons and other small white dogs. It usually is allergies, with them.

One thing which helps: soak each paw in warm water with epsom salts, 3 minutes each. I've never done it, seems a huge bother!

Try to isolate the allergy. Is this happening all year round? Then it is more likely to be food related, assuming you feed the same food consistently. If it is not year round, less likely to be food related.

Sugar does this every year from late Sept to about January. I haven't been able to figure out why; YET. Working on it. With white dogs, the salt in the saliva makes the white hair turn pink! and you can't wash that out, you have to wait for it to grow and then cut it off.

One easy thing to try: switch to metal food bowls, and use distilled water for drinking. I have one friend with a bichon, switching from the tap water to distilled water did the trick.

Wish I could be more helpful.