21 C.F.R. § 73.2190 – Henna.

(a) Identity. The color additive henna is the dried leaf and petiole of Lawsonia alba Lam. (Lawsonia inermis L.). It may be identified by its characteristic odor and by characteristic plant histology.
(b) Specifications. Henna shall conform to the following specifications:
It shall not contain more than 10 percent of plant material from Lawsonia alba Lam. (Lawsonia inermis L.) other than the leaf and petiole, and shall be free from admixture with material from any other species of plant. Moisture, not more than 10 percent. Total ash, not more than 15 percent. Acid-insoluble ash, not more than 5 percent. Lead (as Pb), not more than 20 parts per million. Arsenic (as As), not more than 3 parts per million.
(c) Uses and restrictions. The color additive henna may be safely used for coloring hair only. It may not be used for coloring the eyelashes or eyebrows, or generally in the area of the eye.
(d) Labeling. The label for henna shall bear the information required by § 70.25 of this chapter and the following statements or their equivalent:
“Do not use in the area of the eye.” “Do not use on cut or abraded scalp.”
(e) Exemption from certification. Certification of this color additive for the prescribed use is not necessary for the protection of the public health and therefore batches thereof are exempt from the certification requirements of section 721(c) of the act.