A family holidaying in Cornwall fear their eight-year-old son may have been permanently scarred by what they thought was a harmless henna tattoo.
A burn developed on Nathaniel Fuller's back within days
Nathanial Fuller is having daily hospital treatment for a back burn after getting the tattoo in St Ives.
The artists trading under pedlars' licences in the town say they do warn people about allergic reactions to the chemical dyes they add to the henna.
But the Fuller family, from Hull, have said better regulation is needed.
Father Steve Fuller said most people assume henna is a safe product and has claimed the street artists are acting irresponsibly.
Nathaniel's tattoo cost £7, but within days a burn had developed on his back.
Mr Fuller said: "First of all there was the reddening then it scabbed over and Nathaniel complained it was a bit itchy.
"Then a couple of days later there was some small blistering and within four days it turned into one large blister and the medic related it to a second degree burn."
"The full area where the henna's been applied is oozing pus from the blister which runs down Nathaniel's back.
Nathaniel's brother Jacob also had a henna tattoo at the same time, but he has suffered no allergic reaction.
The trader who applied the tattoo to Nathanial's skin admitted that hair dye is added to the natural henna to make it black and also to make it last longer, but said there is a warning on price boards.
Nathaniel paid £7 for his tattoo on holiday in St Ives with his family
The woman, who did not want to be named said: "Henna comes in red and brown and to get it any other colour you need to mix it.
"Natural henna comes from a plant, so people are not getting allergies from henna, but from the dye."
The trader said parents of children who want a tattoo are offered an allergy test, but only about 40% have the test done.
Penwith District Council says a pedlar's licence can be issued by any police force and allows people to trade anywhere in the country.
Simon Mansell said the council's powers were not strong enough.
"We cannot regulate people such as henna tattooists and we do have concerns on health grounds and safety grounds."