Trauma: This is often the most common cause of soft tissue swelling, resulting from injuries such as falls, blows, or other forms of physical harm. The swelling is usually localized to the area of injury.

Infection: Bacterial or fungal infections can cause soft tissue swelling, especially if there's an open wound or a break in the skin. Cellulitis is a common example.
Inflammatory Conditions: Conditions like rheumatoid arthritis, gout, or pseudogout can cause soft tissue swelling due to inflammation.
Allergic Reactions: Allergic reactions to insect bites, certain medications, or substances can lead to soft tissue swelling.

Deep Vein Thrombosis (DVT): Although less common, DVT can cause swelling in the affected limb and is a potentially life-threatening condition if not treated promptly.
Necrotizing Fasciitis: A severe infection that destroys tissue under the skin, requiring immediate medical attention.
Compartment Syndrome: A condition resulting from increased pressure within a muscle compartment, which can lead to muscle and nerve damage if not treated promptly.

Lymphedema: A condition characterized by chronic swelling due to impaired lymphatic drainage, often secondary to surgery, radiation, or infection.
Lipoma or Other Soft Tissue Tumors: Benign or malignant tumors can cause soft tissue swelling, though they are less common causes.
Sarcoidosis: A disease that can cause inflammation and swelling in various parts of the body, including soft tissues, though it's relatively rare.