Five months baby always love open mouth may be physiological phenomenon, usually normal, but also may be caused by pathological factors such as laryngeal cartilage dysplasia, usually not normal. 1. physiological phenomenon: the baby due to habit, may lead to often open mouth to sleep, just need to see each time, try to correct on the line, need to try many times, in order to slowly correct the habit, is generally normal physiological phenomenon. 2. Laryngeal cartilage dysplasia: baby laryngeal cartilage dysplasia can appear at night snoring phenomenon, a little more serious baby feel breathing effort, it is possible to open the mouth to try to inhale more air, is not normal. Five-month baby always love open mouth may also be caused by deviated nasal septum, rhinitis, etc., to rule out physiological causes, need to seek medical attention as soon as possible to find the cause of the cause of treatment.