Fingernails are four times thicker than the typical strand of hair and often capture more of a substance than hair can and can be detected up to 6 months after drug or alcohol abuse.
What time period does hair testing cover?
The typical length of head hair tested is 1½ inches from the root end. Since the average growth rate of human head hair is approximately ½ inch (1.3 cm) per month a hair analysis covers an approximate 90 day look-back time frame. Hair may be retrieved from the face, chest, and underarms as well.