When using hair for a nutritional/toxic element analysis, we prefer scalp hair because it provides the most accurate metabolic record. Scalp hair is one of the most metabolically active tissues and grows at a more consistent rate than axillary hair (underarm), pubic hair, or other body hair.
In situations where there is insufficient scalp hair you can use axillary hair, pubic hair, or other body hair. Note, however, that samples from the scalp and different parts of the body should not be mixed together.