A stiff tongue may be caused by physiological factors, metabolic diseases, neuropathy, brain lesions and other factors. 1. Physiological factors: Eating a lot of cold and spicy food may cause the tongue to be a little numb and a little wooden, which belongs to physiological factors and can usually return to normal by itself. 2. Metabolic diseases: For example, hyperthyroidism or hypothyroidism may cause edema of the mucous membrane of the tongue, which will make the tongue hard. 3. Neuropathy: For example, hypoglossal neuropathy may affect the nerves innervating the tongue, which may cause the tongue to become numb and hard, and also lead to a decrease in the flexibility of the tongue. 4. Brain lesions: For example, cerebral infarction or cerebral hemorrhage may damage the nerves that innervate the tongue, causing the tongue to become stiff and weak. If your tongue is a bit hard and accompanied by other abnormal manifestations, you should be alerted to the disease factor, and it is recommended to consult a doctor for examination and treatment.