Apart from being useful in a biological sense, hair has properties which make it useful in some other, rather surprising situations. For example, hair samples can be analysed for particular elements to determine whether or not a person was at the scene of a crime. Also, hair samples can be used to test for drug usage in a person. When a drug is in the blood supply of a person, it becomes taken up into the hair at the root level and the hair provides evidence of any drug usage in that person.
Each cm's growth of hair represents a month's worth of blood supply taken up into the hair. Hair samples are usually taken from the head as it grows at a quicker rate and more blood is available for uptake.
Hair's propensity to take up oil into it's structure means that clippings can be collected together and used to stop the spread of oil slicks in oceans.