This has me confused. Why would the study claim it was from the scalp hairs, did these test subjects apply the retin a to their scalp? Can retin a areas of the body or head that it has not been physically applied to?
This has me confused. Why would the study claim it was from the scalp hairs, did these test subjects apply the retin a to their scalp? Can retin a areas of the body or head that it has not been physically applied to?