problem

At least once a year my left or right foot itches terribly.  A hard spot appears (under the arch) which then develops into a blister.  This stays very itchy for several days then dries up forming a scab which finally disappears.  I have had this for many years.  Advice please.

[Yena H Do, DPM]

it may be contact dermatitis.  does this happen when seasons change and you wear different shoes?  you may be allergic to a resin/dye/or material (such as rubber).
if no to the above, you may have vesicular tinea pedis: athlete's foot.    if it doesn't resolve or worsens, consider having the lesion biopsied to confirm the diagnosis.