Some henna artists use PARA-PHENYLENEDIAMINE (PPD) to make “BLACK HENNA”. This can cause severe allergic reactions, blistering and permanent scarring. It can also lead to permanent health problems and life threatening sensitization to a whole class of chemicals including those typically used in households.
NEVER get a black henna tattoo.
TO KNOW WHETHER THE HENNA YOU ARE CONSIDERING IS SAFE, YOU MUST ASK!
Do you use safe natural red henna?
Do you make your henna paste yourself?
What are the ingredients? If an artist cannot list the ingredients, or the ingredients are anything other than 'henna powder, lemon juice, some kind of sugar, and some kind of essential oils, WALK AWAY. DO NOT GET A HENNA.
The unrefrigerated shelf life of natural henna is 3-7 days. If it was mixed and shipped from somewhere far away chances are it will not stain your skin, and if it does it contains a PPD-based dye and/or some other chemical additives plus henna. Some chemical additives in addition to PPD include butane, hexane, kerosene mercuric acetate. These chemicals are DANGEROUS to apply to skin. Some specialty store sell henna cones that may seem like a bargain, but if the cones you are buying are not refrigerated or frozen, and do not come with handling instructions to keep the henna cold - odds are that you are holding chemically augmented henna that can really harm you.