Hello,
Without examination,confirming a diagnosis is tough but it can be granuloma annulare(bumps appearing on the hands) but other possibilities that should be kept in mind are myxoid cyst(growth usually occurring on the finger) , contact dermatitis and dyshidrotic eczema(an itchy rash limited to the hands (usually the palms and sides of the fingers),it can be related to weather and consists of small fluid filled blisters).
I sincerely advise you to consult a dermatologist and get this bump examined to rule out the above possibilities one by one and form a confirmatory diagnosis.Treatment is different for all.
Hope it helps.Take care and pls do keep me posted on how you are doing or if you have any additional queries.Warm regards.
May be a mild callus formation and nothing else.