Can passive smoking of cannabis show on a hair test?
To the contrary --
Hair was once thought to record evidence of drug ingestion like
rings on a tree. Decades of research has shown that external drug
contamination can penetrate hair when moistened and cause the hair
test to incorrectly identify the individual as a drug user. For
this reason among others, the United States governmental agency
charged with drug testing oversight has refused to authorize hair
as a method of drug testing. They have published their concerns in
the Federal Register. Commercial entities, for obvious reasons,
continue to promugate misleading information about hair testing
reliability.