Hi, it could either be yeast in the paws, or an Interdigital Cyst, if it is a yeast infection it can be caused by a food allergy, and you can great it by soaking the paws in warm water and apple cider vinegar, or Epsom salts. If it is an Interdigital Cyst, JeannieCo wrote an excellent article on these cysts, what they are, and how to treat them.
Here re is the link to that article. I hope Dexter feels better soon.
English Bulldog News Forums - Interdigital Furuncle / Interdigital Cyst