According to Mayo Clinic, there are two primary causes for swelling in the legs: fluid buildup or inflammation. Factors relating to swollen legs range from minor to severe.
Mayo Clinic identifies several contributing factors to fluid retention in the legs, known as peripheral edema. On the minor range of the scale, fluid retention is related to pregnancy or prolonged standing. However, it may also be related to more severe factors. Seek medical care if your leg swelling is accompanied by sustained chest pain, difficulty breathing, dizziness or confusion.
Swelling in the legs may also be related to inflammation in the leg tissues. Seek medical treatment if your swelling is the result of a physical injury. Swelling unrelated to physical trauma could be an indication of cellulitis or joint damage related to degenerative factors. Mayo Clinic advises seeking immediate medical care if the swelling occurs with no obvious reason.
Mayo Clinic also points out that the cause of swelling in the legs is often easily identified. This is true in the case of physical injury or prolonged use. By considering other symptoms, you can identify when medical treatment is necessary. When in doubt, or when no direct cause can be identified, seek professional care.