Henna is always pure and natural
Check the ingredient list; if the packet contains anything other than Lawsonia inermis, you do not have pure henna! "Compound henna", a mixture of henna and other herbal or artificial ingredients, has been linked to unfortunate chemical reactions with dyed hair due to the presence of metallic salts. Real henna cannot cause green hair; compound henna can. The best-quality, purest henna for dyeing hair is body-art quality henna, usually sold for mehndi.