DNA, the basic unit of inheritance, is a chemically reactive molecule that is easily altered by both endogenous and external factors. Living organisms are constantly exposed to a variety of DNA-damaging substances that can have an impact on health and disease progression. When cells are damaged by DNA, they activate powerful DNA damage response (DDR) pathways, which give certain DNA repair pathways enough time to physically remove the damage in a substrate-dependent manner. Each parental strand acts as a template for the synthesis of a new complementary daughter strand in DNA replication, which is a semiconservative process.
Many diseases are linked to damage caused by invading pathogens, either directly or indirectly. Although some infections do not cause harm to the host, it is typically a natural result of the pathogens' production of virulence components in order to aid survival, proliferation, and transmission to another host. Cell damage (also known as cell injury) is a type of stress that a cell experiences as a result of both external and internal environmental changes. Physical, chemical, viral, biological, dietary, or immunological variables, among others, might cause this. Damage to cells can be either reversible or irreversible.