What would cause a finger to swell all of a sudden?

Sudden finger swelling can occur due to various reasons, including an injury like a sprain or fracture, an allergic reaction to a substance like food or insect bites, or an infection such as cellulitis. Inflammatory conditions, such as Arthritis or gout, can also lead to rapid swelling. If the swelling is accompanied by severe pain, redness, or fever, it's important to seek medical attention.