Brief Answer: different causes Detailed Answer: HI, thanks for using healthcare magic There are different possible causes such as:(1) cellulitis -this is infection of the skin and the underlying deeper layers. It may also be associated with a fever. There may be a history of a previous insect bite or other small trauma to the leg that allowed the entry of bacteria. This is treated with a course of anti biotics (2) deep vein thrombosis- this is a clot in the deep veins of the leg. There are certain factors that increase the risk of a DVT such as increased weight, clotting disorder, prolonged immobilisation, fractures, major surgery,heart or lung disease This treated with the use of anti coagulants (medication to prevent clotting) (3)trauma to that particular limb (4)allergic reaction to something placed on that limb or an insect bite to that limb. In this case there would be itching. This would be treated with the use of antihistamines (5)heart, liver and kidney disease an also cause swelling but they would normally affect both limbs at the same time To determine the cause, you would need to be examined by a doctor. Though the picture shows the redness and swelling, the definite cause can only be determined by palpation of the limb and investigations. Your doctor may request a doppler- this tests would check for a clot to see if a DVT is the problem Bloods may need to be taken to check for infection. I hope this helps, feel free to ask any other questions

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