I am not involved in running or jumping; I regularly walk on sidewalks and up stairs, but have not been doing *serious* exercise. I wear soft shoes, crepe soles, Clarks, brand, nice insoles.
It is not painful.
It does not seem to be an insect bite. I live in the southwest and thought of that right away, too; but no serious redness, no pain, no evidence of bite or sting...
I am in general good health.
Not a callous.
Ganglion cyst sounds likely.
What causes such a cyst? Is it fluid leaking from the joint? And what causes that?