There are many reasons why thumbs keep cracking, including physiological factors (e.g. environmental dryness, etc.) and pathological factors (e.g. chronic eczema, tinea cruris, etc.). 1. Physiological factors: Due to the dryness of the external air, frequent exposure to wind and sunshine, or the long-term use of alkaline cleansing agents may dry the local skin and cause the thumb to keep cracking. 2. Pathologic factors: (1) chronic eczema: eczema is an inflammatory disease of the skin caused by a variety of internal and external factors. Chronic eczema will appear as mossy skin, rough and flaky, cracked and itchy, which will cause the thumb to keep cracking. (2) ringworm: fungal infection caused by superficial skin inflammatory diseases, especially scaly keratinized ringworm, mainly manifested as thickened keratinization of the skin on the hands, accompanied by flaking, cracking, etc., may also lead to the thumb has been cracked. Thumb cracking may have other causes, it is recommended that patients go to the hospital for examination, clear diagnosis and follow the doctor’s instructions for treatment.