This book presents cutting-edge insights into formaldehyde, with a particular focus on endogenous formaldehyde, revealing its many key roles in the human body. It delves into the relationship between endogenous formaldehyde and cognition, as well as age-related cognitive impairment. It discusses different aspects such as formaldehyde metabolism, its function in the brain, links with epigenetics and neurophysiology, and epidemiological and clinical investigations. The author also provides suggestions on how to prevent cognitive impairment caused by excessive endogenous formaldehyde. This book appeals to all readers who are interested in cognitive science and toxicology. This updated edition significantly expands upon the 1st edition. The author adds five new chapters to broaden and deepen the progression and knowledge of formaldehyde and cognition in recent years. .