RBCs for transfusion are chilled in a preservative solution, extending their shelf life. Most commonly used preservation solutions, such as saline-adenine-glucose-mannitol (SAG-M), allow for refrigerated storage of RBCs for up to 42 days after collection. Alternative solutions such as dimethyl sulfoxide or hydroxyethyl starch may have shorter durations of effectiveness. Once removed from the donor, the red blood cells are washed three times with saline to remove any contaminating white blood cells or other substances that could cause an allergic reaction when given back to the donor. The cells are then suspended in additive solution and frozen into pellets called "straws." These straws are stored in nitrogen vapor until they are needed for an emergency transplant. The use of nitrogen prevents oxidation of the red blood cells while they are frozen and also helps prevent contamination from other things that get stuck in the nitrogen tank. The number one reason people give up blood donation is because they do not feel comfortable having a needle inserted into their arm. However, many modern methods have been developed to reduce the discomfort associated with blood donations. For example, the use of anti-nausea/vomiting drugs reduces feelings of nausea after the procedure and ice packs can be applied to the area after the needle is removed. Most often, blood is donated by volunteer donors who benefit medically by providing blood products for patients in need.