Histone Demethylases (HDMs) comprise the LSD and JmjC families and primarily regulate gene expression within the cell nucleus. These enzymes influence chromatin structure and function by removing methyl modifications from lysine residues of histones, thereby modulating the activation or repression of genes. HDMs participate in numerous biological processes, such as cell differentiation, proliferation, and DNA damage repair. They exhibit specific expression patterns in different tissues and developmental stages, and their dysregulation or gene mutations are associated with health issues like cancer and neurodegenerative diseases. The activity and selectivity of HDMs are intricately regulated by complex signaling networks, highlighting their crucial role in life processes.