Black bruises on the thumbs are considered to be caused by trauma, nevus of nail and venous thrombosis, which can be treated by oral medication and physical therapy. 1. Trauma: local trauma will lead to subcutaneous capillary rupture bleeding, excessive accumulation of blood in the local area will lead to black bruises on the thumbs, accompanied by obvious pain. You can take the capsule to treat it. 2. Nail mole: If the black bruise on the thumb lasts for a long time and there is no itching and pain, it may be due to the nail mole, which can be surgically removed if necessary. 3. Venous thrombosis: If venous thrombosis occurs in the feet, it will lead to a large amount of blood pooling in the toe area, resulting in black bruises on the thumbs of the patients. You can take anticoagulant drugs, such as warfarin sodium tablets. There may be other reasons for the black bruises on the thumbs of the feet, it is recommended to consult a doctor in a timely manner and follow the doctor’s instructions to standardize the treatment.