Two Missouri sisters on a weekend trip with their dad thought it might be fun to get temporary tattoos at a roadside shop, but their amusement turned to apprehension when the black henna wouldn’t come off their skin, MyFOXKC.com reported on Thursday.

Doctors say Emily and Megan Riley, 11 and 15, likely will have permanent scarring after an allergic reaction to the black henna tattoos that were painted on their skin during an outing to Branson, Mo.

Black henna is different than traditional herbal henna in that it contains a toxic chemical called PPD, which usually is found in hair dye, MyFOXKC.com reported.

"Problem is, when people get it on their skin, the skin is a much more sensitive organ than the scalp hair and when it's on the skin in the form of this 'black henna' tattoos, it can cause really bad allergies," Dr. Daniel J. Aires at the University of Kansas Medical Center said in the story.

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