Due to the very low temperatures required, varying levels of stress are put on the DNA samples. Spermatozoa, in particular, are stressed by temperature shock, osmotic stress, and oxidative stress with the latter being the most detrimental. When temperature shock occurs, the membrane is damaged through freezing and thawing of the sperm. Osmotic stress occurs when ice crystals form inside the nucleus during the freezing process, causing differing osmotic pressures within the cell. Oxidative stress is the result of too many reactive oxygen species (ROS), which is highly reactive and damaging to all parts of the cell. Although these stressors are present within the cell, there are solutions to each. By introducing cholesterol to the samples, temperature shock can be reduced. The use of antifreeze proteins provides one solution for osmotic stress. Oxidative stress is the most difficult to combat because of the highly reactive components of ROS, but some measures like adding certain proteins to limit freeze-thaw damage and increase the survival rate of the DNA.