Painful red tongue due to discomfort of systemic conditions, such as endocrine and metabolic disorders, and vitamin B deficiency. So, what causes painful red tongue? The following is a brief introduction: 1, chronic tongue tonsillitis: chronic tongue tonsillitis (chronic lingual tonsilitis) or tongue tonsil hypertrophy, mostly from acute tongue tonsillitis recurrent episodes into chronic. Mostly related to chronic inflammation of the upper respiratory tract, excessive smoking and drinking, eating irritating food and the stimulation of harmful gases. It often coexists with chronic tonsillitis, and compensatory hypertrophy of the lingual tonsils may also occur after tonsillectomy. This disease occurs mostly in adults, children are rare. 2.Neuroendocrine tumors: Neuroendocrine tumors are rare and account for less than 1% of all malignant tumors, mostly occurring in the stomach, intestines and pancreas. The most common of these tumors is carcinoid tumor, whose incidence is about 2.5/100000, accounting for 50% of all gastroenteropancreatic neuroendocrine tumors. According to the origin, carcinoid tumors can be divided into foregut (lung, bronchus and upper gastrointestinal tract up to jejunum), midgut (ileum and appendix) and hindgut (rectum and rectum). Such tumors can occur throughout the neuroendocrine system, but the most common site of involvement is the pancreas. Oral ulcers: Oral ulcers, also known as “mouth sores”, are superficial ulcers on the oral mucosa, ranging in size from rice grains to soy beans, round or ovoid, with concave ulcer surface and surrounding congestion. The ulcers are periodic, recurrent and self-limiting, and are usually found on the lips, cheeks and tongue. The etiology and causative mechanisms remain unclear. Causes may be local trauma, stress, food, drugs, hormonal changes and vitamin or trace element deficiencies. Systemic diseases, genetics, immunity and microorganisms may play an important role in its occurrence and development. Treatment is mainly local and in severe cases systemic treatment is required.