People with autoimmune diseases have been reported to have issues with henna, but its one of those issues where nobody actually seems to agree.
In regards to some Black Henna; (not legal in the states)
Para-Phenylenediamine - One of the most dangerous applications of PPD is when it is added to henna
, a natural dye. When used for temporary tattoos
, henna laced with PPD is known as “Black Henna
.” Although this is not an approved use for PPD in the United States, some tattoo artists will illegally add the chemical to henna for darker temporary tattoos that dry faster than pure henna tattoos. Because the dye is applied while the PPD is in its oxidation
process, its potential as an allergen is increased. Black Henna tattoos often result in a skin reaction similar to a chemical burn, which in turn results in a scar where the skin was tattooed.