Functions of many proteins are regulated by posttranslational modifications. Lysine residue in proteins contains an amino group that is targeted for chemical modifications such as acetylation. Histones are the most famous lysine acetylated proteins, which regulate epigenetic gene expression and thereby determines cell fate. On the other hand, it has recently revealed that lysine residues undergo various acyl modifications including long-chain fatty acylation. These acyl modifications on lysine residues are induced by endogenous carboxylic acids such as fatty acids through chemical reactions in vivo. However, are lysine residues modified by only endogenous carboxylic acids in the body? We are exposed daily to various compounds including carboxylic acids. For example, there are more than 100 types of carboxylic acids in food additives. These exogenous carboxylic acids may be also added to lysine residues of proteins such as histones in the body. In this presentation, we would like to introduce our research on lysine acyl modifications including especially long-chain fatty acylations in transcriptional factors and discuss possible influences of exposure of exogenous carboxylic acids to a living organism from the perspective of lysine adduct exposome.