There's lots of fuss about henna tattoos because an 11 year old girl has been scarred after she had an allergic reaction to the ingredients. But don't worry too much, allergic reactions to henna tattoos are pretty rare.

What are the different types of henna?

There are two types of henna used in tattoos. The first is pure brown henna. This is pretty harmless to skin and hair.

However, there is also black henna, which people can have a bad allergic reaction to. Black henna is made by mixing henna with a chemical dye called PPD. PPD is also used to make some black hair dyes.

The Law about PPD:

There are strict European rules about using PPD, it must not make up more than 6% of the black henna being used. If it is, the tattooist is breaking the law.

Doctors have found the really bad henna scars have been where the PPD was too concentrated.

How can I know if the tattoo is safe henna?

Unfortunately, anyone using the dodgy black henna is probably going to be a bit dodgy themselves and not tell you the truth if you ask them.

Things to look out for when getting a henna tattoo:

• If the dye used is jet black and stains the skin really quickly, then it's probably PPD black henna.
• Ask how long you should leave it on. If the answer's less than an hour, then they're using PPD. Real henna takes much longer. Most respectable artists will ask you try to keep the paste on overnight.
• Ask what colour the tattoo will be when the paste comes off. If the answer is black and the paste is black, then it's PPD henna. Pure henna will leave an orange stain that will go brown, but it will NOT be black when the paste flakes off.
• Ask how long the tattoo will last. PPD black henna lasts a week, henna lasts 1-3 weeks and safe black body dyes last less than three days.
• Ask what's in the mix. A decent artist will tell you: henna, lemon juice and essential oils. A dodgy one will lie. You should be able to smell the oils or lemon juice in the paste.

If you're still unsure, walk away. There'll always be another chance to get a henna tattoo, so it's not worth the risk