Thick fleshy part of the root of the thumb hurts when pressed may be caused by trauma, tenosynovitis, arthritis, infection in the deep interstitial space of the palm and other etiologies. 1. Trauma: If there is a history of trauma, it may lead to injuries in the metacarpophalangeal joint area, ligaments, bones and other parts of the body, which may cause obvious pain at the root of the finger, accompanied by swelling, localized restriction of activities and other symptoms. 2. Tenosynovitis: aseptic inflammation of the flexor tendons of the fingers caused by prolonged and over-exerted activities of the fingers, which is mainly manifested by localized pain, pressure and pain, and limitation of the activities of the affected joints. 3. Arthritis: the cause of the disease is still unclear, may be related to age, heredity and other factors, mainly manifested as localized redness, swelling, heat and pain. If it occurs in the hand, it will lead to pain when pressing the fleshy part of the root of the thumb. 4. Deep interstitial infection of the palm: the cause of the disease is related to the spread of tenosynovitis of the middle finger and ring finger, direct stabbing, etc. The patient will have symptoms such as disappearance of the normal depression in the center of the palm of the hand, bulging, and obvious pressure and pain. There are many reasons why the root of the thumb hurts when pressed, and it is recommended that patients go to a regular hospital for a relevant examination to clarify the cause of the disease.