The typical lifespan of red blood cells (RBCs) in a healthy adult is around 120 days, but that of transfused RBCs is about 50–60 days and can be much lower in the presence of conditions limiting their survival. Transfusion with older RBCs increases the risk of developing bacterial or viral infections. In general, the life span of transfused RBCs depends on how they were stored before use. Storage time has a major impact on RBC quality and viability, so it is important to choose an appropriate storage method for different types of RBC products. For example, frozen RBCs can only be stored for approximately six months, while refrigerated RBCs can be kept for up to one year. The life span of transfused RBCs can also be extended by chemical additives present in some storage solutions. However, these additives may not be necessary for some types of RBC products. Finally, the life span of transfused RBCs can be shortened if they are irradiated prior to transfusion. Irradiation kills most pathogens present on donated blood products, preventing transmission of infectious diseases. It does this by breaking down DNA into fragments that cannot be re-built by the body's natural repair mechanisms. Radiation also has other effects on RBCs that increase their elimination rate from the body.