The tongue is thick and thin on one side due to the following reasons: 1. brain neuropathy, brain neuropathy can result in facial nerve damage causing facial palsy on one side, so that the nerves that govern the tongue will also change accordingly, resulting in atrophy, thinning and small tongue on one side, for example, cerebral infarction may lead to such consequences. 2. local lesions of the tongue, if the tongue has a corresponding lesion, it may lead to thickening on one side. For example, if there is edema after tongue infection or tongue bite, the above symptoms may occur. 3, diet or allergy factors, long-term use of the lower teeth chewing food or long-term consumption of spicy, allergy-prone food, may lead to thickening of one side of the tongue. If the tongue appears to be thin on one side and thick on the other, you should go to a regular hospital for relevant examination in a timely manner and use the correct treatment under the guidance of the doctor according to the examination results.