Ankle Sprain: This is the most common cause of lateral foot swelling, often resulting from inversion injuries that stretch or tear the ligaments on the outside of the ankle.

Peroneal Tendinopathy: Inflammation or degeneration of the peroneal tendons, which run along the lateral side of the ankle and foot, can cause swelling and pain in this area.
Lateral Foot Fracture: Fractures to the bones on the outside of the foot, such as the cuboid or fifth metatarsal, can lead to swelling and may be caused by direct trauma or stress fractures.
Gout or Pseudogout: These conditions can cause sudden, severe swelling and pain in the foot, including the lateral side, due to the deposition of urate or pyrophosphate crystals within the joints.

Compartment Syndrome: A serious condition where increased pressure within the muscle compartments of the foot can lead to nerve and muscle damage. It requires urgent medical attention.
Deep Vein Thrombosis (DVT): Although less common in the foot, DVT can cause swelling and requires immediate medical evaluation to prevent potentially life-threatening complications like pulmonary embolism.
Infection (Cellulitis or Abscess): Bacterial infections can cause swelling, redness, and warmth in the affected area. In severe cases, they can lead to sepsis if not promptly treated.

Erythromelalgia: A rare disorder characterized by burning pain, heat, and redness in the hands and feet, which can also cause swelling.
Complex Regional Pain Syndrome (CRPS): A condition that can follow an injury and is characterized by chronic pain, swelling, and changes in skin temperature and color.
Tumor (Benign or Malignant): Although rare, tumors can cause swelling in the foot. Examples include soft tissue sarcomas or metastatic disease to the foot.