A thrombus normally forms because of one or many of the following factors: Immobility: Immobility can be a potential cause of deep vein thrombosis. Immobility can occur in long air, car or train travels which cause prolonged sitting, thus restricting the necessary movement and mobility. Other situations in which people commonly become immobile are when they get hospitalized or go when through a surgery. Pregnancy and obesity also limit mobility. Hypercoagulability: Hypercoagulability occurs when the speed of blood’s coagulation increases. This may happen because of smoking, cancer, medication of any sort, genetic predisposition or increase in the amount of red blood cells in the body. Vein trauma: Vein can experience a trauma in case of fracture or bruises on the leg. Symptoms: Trauma experienced by the vein is the most common cause of clotting of blood in superficial vein system. In the deep venous thrombosis, symptoms are related to the hindrance to the flow of blood from different body organs to the heart. This causes the vein and the skin around it to undergo inflammation. Symptoms of deep venous thrombosis include, but are not limited to excessive warmth, swelling, redness and tenderness on the skin. The patient feels pain in the specific regions on the skin where the symptoms show up.