Hi, An intense burning sensation and discoloration under the nail of your big toe may be due to several different conditions, including: * Ingrown toenail: When the toenail grows into the skin, it can cause pain, swelling, and redness. In severe cases, an infection may develop, leading to discoloration of the nail. * Fungal nail infection: A fungal infection of the nail can cause discoloration, thickening, and brittleness of the nail. It may also cause a burning or itching sensation under the nail. * Trauma or injury to the nail: An injury to the nail, such as stubbing your toe or dropping something heavy on it, can cause a burning sensation and discoloration under the nail. * Paronychia: An infection of the skin around the nail can cause redness, swelling, and pain, as well as discoloration of the nail. * Gout: Gout is a type of arthritis that can cause sudden and severe pain, swelling, and redness in the joint. It can also cause discoloration of the nail. See a doctor and get proper diagnosis and treatment. Treatment options may include antibiotics, antifungal medications, or in severe cases, surgical intervention. Proper foot care and wearing shoes that fit properly can also help prevent these conditions. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician