Why have my leg veins suddenly become very visible?

Venous insufficinecy: Visible veins on the legs are usually the result of venous insufficiency. The insufficiency may be in the skin [resulting tiny spider veins], or below the surface of the skin [ causing tiny and varicose veins] or in deep veins. It is best to have this evaluated by a vein specialist, often with aid of an ultrasound to see how best to treat. Weight loss or fat loss also makes veins more visible.