Hair drug testing can detect drug use over a much longer period of time,[19] which is often used for highly safety-critical positions where there is zero tolerance of illegal drug use.[20] Standard hair follicle screen covers a period of 30 to 90 days. The growth of hair is usually at the rate of 0.5*inches per month. The hair sample is cut close to the scalp and 80 to 120 strands of hair are needed for the test. In the absence of hair on the head, body hair can be used as an acceptable substitute.[19] Even if the person being tested has a shaved head, hair can also be taken from almost any other area of the body. This includes facial hair, the underarms, arms, and legs or even pubic hair.