The causes of red tongue may be food, fungal infections, localized ulcers and so on. 1. Food: If you consume spicy, irritating or too hot, too hard food, it may cause red tongue due to chemical or physical stimulation; or consume food with red coloring such as red dragon fruit, which will stain the tongue red. 2. Fungal infection: Fungal infection can cause fungal stomatitis inside the mouth, which leads to redness on the surface of the tongue, the main clinical symptoms are redness and swelling of the tongue, oral mucosa, and the formation of white patches of pseudomembrane. 3. Localized ulcers: ulcers of the oral mucosa can also be manifested as localized redness and swelling of the tongue, accompanied by pain, and sharp tips of buds or dental calculus, etc., can also scrape the mucous membrane of the tongue, forming ulcers. If there is a red tongue, and can not be relieved by themselves, you can promptly consult a doctor.