A yellowish layer on the top of the tongue may be related to hyperpigmentation, mouth ulcers, poor oral hygiene and other reasons. 1. Hyperpigmentation: If you consume beverages and food with yellow coloring, it can cause a yellowish layer on the top of your tongue. 2. Mouth ulcers: due to bacterial infection, mouth ulcers are covered with a yellowish pseudomembrane on the surface of the ulcers. 3. Poor oral hygiene: If you don’t pay attention to oral hygiene, food residue can be trapped in the papilla of the tongue, causing a yellowish layer on the tongue. It is recommended that people with a yellowish layer on top of the tongue go to the hospital in time to clarify the cause, and if treatment is needed, standardized treatment should be carried out under the guidance of the doctor to avoid delaying the condition.