Beware black henna

I found the "What's That Stuff?" on henna (C&EN, Feb. 6, page 28) of great interest, but it is very important to note the difference between traditional natural henna temporary tattoos, the subject of your article, and temporary tattoos made using so-called black henna. As stated in the article, the latter may contain high concentrations of p-phenylenediamine (PPDA), which is a very potent skin sensitizer leading to cases of severe allergies.

According to European Union regulations, PPDA should not be applied to the skin except as a component of hair dyes and with a maximum concentration of 6%. Black henna temporary tattoos are now offered for a few euros or dollars in most tourist areas and are very popular among children, teenagers, and young adults. Numerous cases of very severe contact allergies have already been reported in the medical literature around the world as a consequence of the illegal use of this hazardous chemical.

Once you have been sensitized, it is for life, and any further contact with PPDA or a related chemical will cause severe eczema, so it is important to warn against the use of black henna. Natural henna is never black. This may be less fashionable, but it is much safer.

Jean-Pierre Lepoittevin
Strasbourg, France