Failure to sweat in hot weather may be related to sweat gland dysfunction, ichthyosis and nerve damage. 1. Sweat gland dysfunction: For patients with sweat gland dysfunction, if the sweat glands have problems functioning, then the sweat in the body can not be discharged, and it will be easy to have the symptom of not sweating no matter how hot the day is. 2. Ichthyosis: In addition, patients with ichthyosis skin disease are also prone to not sweating. Because the sweat glands are generally between the subcutaneous tissue and the cortex, and ichthyosis patients’ skin keratinization process is usually faster, which leads to patients’ hair follicles and glandular ducts will be blocked, resulting in sweat can not be discharged normally, thus appearing in the heat of the day does not sweat phenomenon. 3. Nerve damage: because any activity in the human body can not be completed without the control of the nerves, if the control of the sweat glands of the nerves are damaged, can not be effective and timely, to receive the signals of the neurons of the brain, then it is very likely to appear in the heat of the day does not sweat the situation. If the patient does not sweat in the heat of the day and no improvement in the phenomenon, it is recommended that timely consultation to identify the cause of targeted treatment.