There is a story in todays online news that details how a 5 year old is being treated for what is possibly a chemical burn from a henna dragon tattoo. The ink has come off but the welt underneath depicts the outline of the dragon!! It is not so temporary.
There is a picture here. Please be careful and know the product being used. http://www.goldcoast.com.au/article/2009/06/08/86241_gold-coast-top-story.html