Trauma or Injury: This is the most common cause of a swollen finger, often resulting from a direct blow, crush injury, or a fall. The swelling can be due to bruising, hematoma, or fracture.

Infection (Paronychia or Felon): Bacterial infections can cause swelling, redness, and pain in the finger, often related to a break in the skin or an ingrown nail.
Allergic Reaction: An allergic reaction to an insect bite, certain foods, or substances can cause localized swelling in a finger.
Arthritis (Osteoarthritis or Rheumatoid Arthritis): Although less common in a single finger, arthritis can cause swelling, especially if there's a history of similar symptoms in other joints.

Compartment Syndrome: A serious condition that occurs when pressure within the muscles builds to dangerous levels, reducing blood flow. It requires immediate medical attention to prevent permanent damage.
Necrotizing Fasciitis: A rare but life-threatening infection that can cause swelling, pain, and discoloration. Early recognition and treatment are crucial.
Osteomyelitis: A bone infection that can cause swelling, pain, and redness in the affected finger, requiring prompt antibiotic treatment.

Gout: Although more commonly associated with the big toe, gout can cause sudden, severe swelling in any joint, including the fingers.
Sarcoidosis: A condition that can cause inflammation and swelling in various parts of the body, including the fingers, though this is less common.
Tendinous or Ligamentous Injuries: Injuries to the tendons or ligaments, such as a mallet finger or a ligament sprain, can cause swelling and require specific management to prevent long-term dysfunction.