Hello and welcome to HCM
A painful swelling on underside of the heel can be a 'corn'.
A corn is formed due to proliferation of upper layers of the skin. It is a harmless lesion and treatment consists of removal of the corn.
This swelling can be due to bony growth or any other soft tissue
X-ray of the foot will determine whether the swelling is arising from the bone or soft tissue.
Exact diagnosis can only be made by clinical examination and investigations.
Consult your doctor for further management.
Thanks and take care
Dr Shailja P Wahal