People vary in their ability to tolerate the sight of blood and their squeamish response to gory details. There are also the religio-spiritual attributes of blood and blood shedding preserved in ritual and customary behaviour in practices as varied as hunting, birth, injury, cleanliness, and food taboos. Whilst certain people and groups (e.g. Jehovah's Witnesses) have consistently refused blood transfusion as a medical intervention, fear of receiving blood from another person has grown markedly with the scare over AIDS, ironically at a time when blood transfusion technology has reached a very high level of safety.
One third of Americans blood donors have stopped donating blood through risk of infection by AIDS (totally unfounded). Five percent of people now donate their own blood prior to an operation compared with a negligible number of mainly rare blood types who previously undertook so called autologous blood donation. The concern has also modified surgical procedure. Spilled blood is now often collected from the patient by suction rather than disposable sponges so that it can be processed and returned later in the operation, sometimes diluted with a neutral blood expander. In addition surgeons now will allow a patient's blood count to drop to unprecedentedly low levels before they call for a transfusion. A major biotechnology expansion is underway to develop blood substitutes by genetic engineering of pigs, cows blood, reprocessing outdated human blood and artificial haemoglobin made from perfluorocarbon, a relative of teflon.