Histone deacetylase inhibitors (HDAC inhibitors) are a class of compounds that block the activity of histone deacetylases, enzymes involved in modifying the structure of chromatin. By inhibiting these enzymes, HDAC inhibitors promote the acetylation of histones, leading to a more relaxed chromatin structure and increased gene expression. This mechanism can influence various cellular processes, including cell cycle regulation and apoptosis. HDAC inhibitors are being studied for their potential therapeutic effects in several conditions, particularly in cancer treatment. They can enhance the effectiveness of other therapies and may help in the treatment of neurodegenerative diseases and inflammatory disorders by altering gene expression patterns associated with these conditions.