Saliva is functional water that affects the entire body. The author has been focusing on the functionality of saliva and has been proposing a new concept of saliva “quality” for more than 10 years. Saliva should then be viewed in terms of both quantity and quality. The author found that expression of the brain-derived neurotrophic factor BDNF is induced in salivary glands during stress. Furthermore, they found that salivary gland BDNF increases plasma BDNF levels via the oral floor region. Salivary gland-derived plasma BDNF may mildly increase BDNF levels in brain tissue and activate hippocampal TrkB receptors, thereby enhancing GABA production and contributing to the maintenance of hippocampal neuronal function from stress. Salivary glands and the brain are also in close proximity as blood flow-mediated root. The results of this study have led us to infer the existence of a salivary gland-brain correlation and have demonstrated new possibilities for the salivary glands. Now, salivary BDNF research, which taught us that salivary components are important for health, has develop a new health concept called “saliva care” and is advancing into a new social activity that contributes to the health of the public.