They're making a comeback. Tattoos are decorating the bodies of celebrities kids love to copy.

But many of them are drawn on — no painful needles etching permanent markings on the body. The artists use ink they call "black henna." They say it's from a plant.

A simple henna tattoo

A simple design takes about 30 seconds and costs about $15. It's cheap and, the artists say, harmless.

But Evan Kirk discovered otherwise while on vacation in Florida. He got a Chinese design painted on his back. A day later, he was in agony.

"I couldn’t really see because it was on my back but you could feel it dripping and I had to put a cloth on it because there was so much puss."

Kirk was told the tattoo was applied using natural henna.

In its paste form, natural henna is green. Once on the skin, it shows up red, orange or brown — never black.

Painting henna on the body is a thousand year old tradition called Mehndi art. Shams Surani has been doing it for 30 years.

"It’s the powder of the henna plant. The plant goes back almost 1,500 years when they used it for different purposes. They used it for self-tanning, dying clothes, and for sunstrokes."

Later, it was used to decorate brides. With the help of movies and magazines, henna art has gone mainstream.

But Evan Kirk did not get pure henna. His black henna tattoo was doctored with a chemical known to irritate the skin. It's called PPD — or paraphenylenediamine. It makes henna tattoos black and longer lasting. But it can also cause serious allergic reactions in some people.

Health Canada warning

Like any allergy, not everyone will react. But the risk is severe enough that Health Canada has banned PPD in cosmetics. In August 2003, Health Canada sent out a warning about black henna tattoos containing PPD. The problem is, most people still don't know that black henna can be harmful and many of the artists underplay the risk.

With a hidden camera, Marketplace visited two black henna booths. At the first one, the artist mentioned possible allergic reactions only after our researcher specifically asked. But at the second booth, a surprising admission:

Artist: Your skin might bubble. You might have a scar there?

Researcher : It might leave a scar?

Artist: You might have a scar.

Researcher: How often does that happen?

Artist: Not that often.

One company makes kids sign a waiver saying they are aware of possible irritations to the skin. Kids sign but generally ignore it. Meantime the message is that it’s pure.

Krystal Craig trust that black henna was harmless, but she learned something different when she got a tattoo at a Toronto exhibition last year.

"I noticed there was like little bumps on it and they were red and itching. And it just kept getting more intense."

Krystal's mother, Deborah, did some research and found warnings about black henna tattoos on the internet.

"We started up a little web page of Krystal’s story and started to circulate it through the e-mails to see if we could get anybody coming forward to share their stories with us."

With testimonials like Krystal's and Evan's, Marketplace decided to test some black henna commonly used in Canada.

Owner-operator Georgia Steel agreed to let Marketplace test her henna

First stop — Body X, a division of Picasso Painters, set up at the Canadian National Exhibition. Owner/operator Georgia Steel says she would do hundreds of tattoos a day at the summer fair. She also said there was no PPD in her black henna.

"What I do know is that now we’re making sure that we’re not using anything unless we have a guarantee from the manufacturer. Gradually as we get rid of the remnants from past suppliers, we bring in the product from the new suppliers."

We asked Steel for a sample, so we could test it. She gave us one.

Next stop was "Little Miss Henna," operating out of large theme parks and shopping malls. When we reached the owner, Melanie Marcus by phone, she was not keen to speak with us.

"You can go and talk to my competitor all you want. I’m not available to be honest with you. I don’t want you talking about me and my company."

Marcus said her product contained no henna, but she would not give us a sample to test.

We got a better reception with aesthetician Shams Surani. She said she sometimes uses black henna. She gave us a sample to test.

And we went to the internet, where you can easily buy black henna for home use.

We spoke to a dermatologist in Toronto — Dr. Paul Cohen — who had this warning about black henna.

'Might cause a problem later on,' says Dr. Paul Cohen

"I think people have to be cautious and be aware that these seemingly innocuous tattoos might potentially cause a problem later on."

That rings true for Evan Kirk. He dyed his hair black, along with the rest of the players on his lacrosse team. He suffered a severe reaction and was in bed for a few days.

What the Kirks did not know was that the same chemical in Evan's tattoo is found in many black hair dyes: PPD.

"What you’ve done by having this tattoo done is you’ve sensitized yourself so you set up your body to make an immune response to this PPD and then when you dye your hair you might develop an allergic reaction later on," Cohen said.

You could potentially set yourself up for trouble down the road with just one or two tattoos.

Our lab tests on black henna showed some PPD. The sample we bought off the internet scored the highest with 10 per cent PPD. Sham Surant's sample showed 1 per cent PPD. As for the sample from Body X — as the owner told us, there was no detectable PPD.

The best advice? Ask if there is PPD in the black henna you're about to try — and ask for proof. Otherwise, you may be one of the few whose flirt with a tattoo turns nasty.

NEXT: Products with PPD »