Mercury thermometer armpit 35.5 degrees is usually a normal physiological phenomenon, but may also be a pathological phenomenon caused by diseases such as dysfunction of the thermoregulatory center, hypothyroidism and so on. 1. physiological phenomenon: some people may be in a cold environment, the body can not replenish heat, resulting in a large amount of heat dispersal, thus causing a body temperature of 35.5 degrees. It is also possible that a large amount of sweat appears on the body after strenuous exercise, and the evaporation of this sweat will emit heat from the body surface, which may also lead to a body temperature of 35.5 degrees. 2. Dysfunction of thermoregulation center: Dysfunction of thermoregulation center refers to the dysfunction of thermoregulation center, which is mostly related to the patients’ excessive application of antipyretic drugs, endocrine disorders and mental overstress, etc., and is mainly manifested in the inability of thermoregulation center to regulate the body temperature effectively. 3. Hypothyroidism: it refers to the decrease of thyroxine secreted by the thyroid gland due to primary or secondary reasons, so it may lead to the patient’s basal body temperature being lower than normal body temperature. The above are only some of the common causes. If the patient has other uncomfortable symptoms, he should go to the hospital immediately to find out the cause of the disease, and carry out standardized treatment under the guidance of the doctor.