Thanks for the plug Birdgirl. They can detect drugs throughout the whole length of the hair but it becomes inaccurate after 90 days so in the U.S. anyway, the standard is only to go back at most 90 days or 1 and 1/2 inches of hair. They will mark the root end of the hair and at the lab cut it down to this length if it is longer than this. If they use body hair, they mark where they got it from and adjust the length based on the growth rates of that body hair, which is usually a little slower than head hair. To test positive, you must smoke 3 times or more during the last 90 days.

Napolitana, shaving your head will result in 3 things:
1) Using body hair
2) Using fingernail shavings
3) Failure do to refusal to submit sample.

I have actually answered this twice now for this new member!