In science and medicine, contact factor is the term used to refer to factor XIII, which is a protein component of the complement system in animals and humans. This factor has the ability to bind to the surface of cells and tissues of the body and protect them from damage and destruction. With its help, cells can quickly respond to various external factors, such as infections, injuries and other damage. One example of the practical use of contact factor is its use in creating vaccines to combat infectious diseases. Currently, contact factors are the focus of research in biology and medicine due to their potential role in the treatment of diseases associated with various disorders of cell interaction.