The common cause of unilateral calf swelling is calf vein thrombosis, when the calf vein thrombosis, there will be calf vein blood reflux is not smooth, in the clinical manifestation of calf swelling, the patient in the pinch the leg belly will appear pain obvious, the skin can be seen on the surface of the skin is bright, touching the skin will be the skin of the sunken oedema, which is the symptom of thrombosis. Uncommon causes are local skin soft tissue causes, such as skin soft tissue infection or muscle, tendon cysts, when the tendon cysts rupture, the fluid will flow to the lower leg of the subcutaneous, can also appear swelling. In addition, there is another reason is mosquito bites, when mosquito bites can also appear skin swelling, the above is the common causes of calf swelling.