Foot edema (AKA swelling) can be distressing symptom. It has too many causes for me to cover completely, but I can give you some broad categories that you can consider. It is a sign that should be evaluated by his primary care physician
who can determine the cause and initiate treatment if necessary. This type of edema happens with fluid gets forced into the tissues from the blood vessels. Probably the most common cause of a little foot swelling is a syndrome called venous insufficiency. As people age, the veins that bring blood from the feet to the heart get stretched out and don't squeeze the blood back to the heart well. As a result, there is back flow resulting in fluid getting stuck in the foot tissues. This can be treated by wearing tight fitting stockings (TED hose). Another possibility is a blood clot in a leg vein. This can cause foot edema by the same mechanism as venous insufficiency (back flow), but usually is only one foot. A blood clot is dangerous because if it dislodges, then it can travel to the lungs which is life threatening. Finally, if your dad has any heart trouble, edema can be a sign of hear failure. Only his doctor
can sort out the many different cause of edema. Thanks for the question.