The blood in veins of our legs normally moves from bottom to top, or from the foot to the thigh and then up towards the heart. Leg veins have one-way valves that enable them to push the blood up the leg against gravity.
When varicose veins appear, it's often because these one-way vein valves are not functioning normally. The valves are not able to resist the constant push of gravity downward, and back-flow occurs. As the back-flow persists, venous blood settles in the lower leg. Hence, the leg swells up as the result of this elevated pressure in the veins, and the swelling tends to be most prominent after you've been standing for a long period of time.
This can also cause calf cramps, skin darkening and even open wounds called ulcers.
If you've got your swelling examined recently and have realized that you are suffering from varicose veins, you need to get a Colour Doppler of the veins of the legs to look for this disease.
Early varicose veins can be treated by wearing Varicose Vein Stockings, symptomatic cases would need treatment like Endovenous Laser Ablation for Varicose Veins (EVLT) or open surgery.
EVLT is a non surgical treatment for varicose veins which gives no scar and the patient starts walking normally the very same day!