Dear user, Thanks for your query. The long red line as you described could be one of the veins inflamed, known as Thrombophlebitis. As you haven t mentioned any history of traveling or injection into your veins, there could be a couple of possibilities which caused it. 1 Insect bite 2 Intravenous injections 3 known vascular diseases eg SLE, Buergers disease 4 Infections around the area eg infected toe nail/ ulcers on lower leg 5 states where the tendency of blood clots increase e.g smoking, pregnancy, contraceptive pills 6 Blood disorders, where blood is naturally thicker and tends to clot within the vessels 7 Varicose veins 8 OR it may arise spontaneously without any underlying cause. Other signs associated with it is that you can feel a cord like vein, actually under the line which you can see. This is usually a self limiting condition, but it is worth going to your doctor to get it checked. Because these superficial veins are connected to a set of deeper veins, under the muscles, so you don t see/ feel them. it is important to make sure that this infection/ clot is not extending into that deep vein system, esp if there is any leg swwelling. as that is a more serious condition. Secondly, you might need some blood tests to make sure that there is no infection in the body that might need antibiotics and then check that clotting/ immune profile is normal as well. Once anything sinister is ruled out, and checked, you can take pain killers and rest as needed until this goes away, which could be a few days. but in the long run, you might have to avoid long standing to decrease pressure on the veins as this condition tends to recur