Research by the European Chemicals Agency has been looking into the dangers and toxicity of tattoo ink on the human body and whether the inks should be regulated.

The agency said: "Many reports show significant concerns for public health stemming from the composition of inks used for tattooing.

"The most severe concerns are allergies caused by the substances in the inks and possible carcinogenic, mutagenic or reproductively toxic effects."

Inks are not currently regulated in the EU. If any particular chemicals are found to be harmful as thought, they will be banned.

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They added: "If it is found that a restriction is needed, a formal proposal to restrict the substances will be submitted within one year to initiate the process."

Research by the agency is to be published imminently and it has revealed that red ink has been linked to dermatitis - swelling and soreness - due to it containing mercury sulphide: "sulfate red has been classified as a carcinogen and as toxic to reproduction."

Meanwhile red, blue, green and purple ones are more likely to cause granulomas - little ridges of bumps on the skin.

In the UK, the National Health Service (NHS) has also warned of the dangers of "black" or "neutral" henna, according to the Independent.

Different to authentic henna, which is orange in colour, this darker substance it may contain levels of a chemical dye "so powerful and toxic that it is illegal to use it on the skin".