This chapter summarizes information about specific chemicals formed during food processing. Overall, it discusses undesirable chemicals that can develop in some foods during processing. These chemicals result from reactions between naturally occurring compounds in food, especially during heat treatments like baking and frying, or under specific storage and processing conditions. A well-known example is acrylamide, used industrially but also forming in carbohydrate-rich foods cooked at high temperatures. Therefore, the chapter provides a brief overview of the chemical and physical properties, usage patterns, main health risks, and toxicokinetics of various substances, along with references to scientific literature. The aim is to summarize detailed information on their presence in human samples such as blood, urine, and breast milk. Particular emphasis is placed on food processing chemicals, including acrylamide, furan and furanic compounds, monochloropropane diol (MCPD), glycidol, melamine and its analogues, and heterocyclic aromatic amines.