Vitamin B deficiency can cause a variety of adverse manifestations such as beriberi, mouth ulcers, irritability and gastrointestinal reactions. 1. foot fungus: usually because of the lack of vitamin B1 manifestation of foot fungus can appear loss of appetite, body weakness, or affect the patient, resulting in mental illness. 2. Mouth ulcers: usually refers to the lack of vitamin B2 manifestations, in addition to mouth ulcers may also appear lip corner ulcers, wound ulcers and other adverse symptoms. 3. irritability: lack of vitamin B6 performance, there may also be excessive secretion of skin oil, hair is also prone to texture is not good, easy to hair loss, can also cause long-term repeated mouth ulcers, patients with mouth sores. 4. Gastrointestinal reaction: the lack of vitamin B12 performance, may appear anorexia, poor digestion and absorption, diarrhea adverse reaction, may also appear weakness, memory loss, distraction and other symptoms. If the above symptoms occur, we should consult the doctor in time to identify the cause and target treatment under the guidance of the doctor.