swelling may be due to Dependent swelling (or edema) like standing or walking for extended periods like salespersons,construction workers, obese individuals, and individuals with underlying health problems like Infection: any person infected, either localized (abscess) or diffuse (cellulitis)of the foot or legs,Lymphedema: Persons with lymph vessel or lymph node blockage of lymph fluid, due to infections, trauma and Blood clot(s): People with blockage of blood vessels (usually venous) that cause fluid to leak out of vessels into tissues. the swelling becomes chronic and the skin becomes more rigid, reddish and sometimes mildly discolored or mottled and will not return to normal after a few hours of elevation. first advice your sun to elevate the legs for few hours. if,still problem will remain same then get blood pressure,blood sugar level test done first.