Why is my foot swelling and turning dark red?

Let try to help: There two mean reasons for that, either got infected or lack of circulations.

See a doctor: If there is no history of injury you need to see a doctor.

Many possibilities: Some causes of swelling of the feet and ankles can include systemic problems such as hypertension, and problems with the kidneys and localized issues such as arthritis, infection, lymphatic obstruction, blood clots, varicose veins, trauma (fracture, sprain, and tendonitis) and side effects to medication. Have it evaluated by a professional and get the appropriate treatment.

The are many causes: For foot swelling, redness can be caused by venous insufficiency, dependent rubor, sometimes infection - you should seek a medical evaluation.