Often, pain on pressure at the root of the thumb can be caused by localized trauma, localized callus or stenosing tenosynovitis. 1. Localized trauma: If the pain at the root of the thumb is present after thumb movement, consider whether it is caused by localized trauma. In general, if it is trauma, it may also be accompanied by symptoms such as limited thumb movement. 2. Localized corpus callosum: If the thumb is rubbed excessively for a long time, it is more likely to form corpus callosum at its root. In the formation of callus, it is likely to lead to localized pain, especially when pressing the root of the thumb. Therefore, it can be considered as the cause of localized callus. 3. Stenosing tenosynovitis: Stenosing tenosynovitis is usually caused by inflammation of the flexor tendon and the tendon sheath, and may also present with pain when the fleshy part of the thumb root is pressed. Stenosing tenosynovitis is often accompanied by limited thumb flexion and extension. If the symptoms of pain on pressure at the base of the thumb are persistent, it is recommended to go to the hospital as soon as possible for a professional diagnosis to avoid delaying the condition.