Henna is the oldest plant name used as cosmetics. Very safe to use. Rarely causes problems. If in doubt because of having sensitive skin, it's good to consult a doctor and try it in small quantities. For example by applying a little henna on the back of the neck or under the arm, because the skin in the area is classified as the most sensitive areas. Natural Henna is usually safe because it contains no chemical synthetic dyes or other harmful additives.

Mehendi blended from a leaf of a plant called Henna or Lawsonia Inermis. Henna can be worn on body parts by creating beautiful patterns and designs. Henna is also known for its healing and therapeutic properties. Since ancient times, henna is used to nourish hair to be more shiny, serves as a hair conditioner and good for the scalp.
Well, that's history about henna.