A red tongue can be caused by physiological factors, lingual inflammation, stomatitis and other factors. 1. Physiological factors: drinking too little water for a long time or eating red dragon fruit and other factors may lead to red tongue, but there are no other clinical symptoms, drink more water, improve daily diet, can be recovered on their own. 2. Tongue inflammation: may be related to fungal infection, vitamin deficiency, poor oral environment and other factors, will lead to changes in the tongue, will make the tongue congested, red and swollen, may also be accompanied by tongue pain, burning sensation and other symptoms. 3. Stomatitis: it may be caused by bacterial, fungal or viral infections, which may cause localized irritation to the tongue, leading to redness of the tongue, which may be accompanied by symptoms such as ulceration of the oral mucosa, edema and pain. A red tongue, accompanied by other obvious abnormalities, should be alerted to disease factors, and recommend medical examination and treatment.