Liz Buchanan BVSc MRCVS
To enlarge on this, there is a massive range of possible diagnoses for a lump between the toes, ranging from skin disease such as demodex mite infestation, wasp sting, autoimmune or allergic skin disease (very common, with swelling of skin secondary to licking or to infection as a result of having being licked, for example), or possibly a lump from licking due to arthritic pain, or underlying bone cancer, or else a foreign body or even a fracture. Another cause might be benign or aggressive skin cancer. Your vet may have to do tests to find out which answer is appropriate in this particular case and may start by ruling out the easiest, or the most likely or most worrying possibilities, depending on their findings. Biopsy, trial treatments or radiography may be proposed. If just one area is being licked, local changes may be suspected; if it is widespread across the digits / feet, skin allergy and secondary problems may be one of the likely possibilities. Best of luck and please let us know how you get on.