Local councils have called for tougher sentences for illegal tattooists, who they warn are offering cheap prices for their services to children.
The Local Government Association (LGA) said the problem was increasing because tattoo equipment was becoming more widely available and cheaper to buy.
The LGA warned that unlicensed tattooists can take "dangerous shortcuts with health and safety".
They may work in unsterilised studios, using cheap equipment bought online.
The LGA has also urged online retailers to provide warnings to children about the dangers of using do-it-yourself tattoo kits, which can be bought for less than £25.
It is illegal for anyone under the age of 18 to be tattooed, unless it is performed for medical reasons by a qualified medical practitioner, or someone working under their direction.
Unlicensed tattooists, also known as scratchers, often work from home in kitchens or garden sheds and advertise their services on social media.
It is illegal to work as a tattooist without registering with the local council.
Checklist for anyone thinking of getting a tattoo
- An establishment should be registered with the local council - if in doubt ask to see the registration certificate or check the council's online database
- Check whether the person you're dealing with has undergone recognised training and qualifications
- Ask to see examples of the person's work
- Ensure that you have read and signed a consent and medical form
- Make sure tattoos are done with new needles. If you don't see the needle removed from a sealed package, don't allow the tattoo to be done
- Check that a proper tattoo ink is being used and that it is sterile at the start of your treatment
- The tattoo artist should always wash their hands and put on a fresh pair of medical-type gloves before each new procedure
- Ensure that you are given advice on the aftercare for your tattoo
LGA Board member Cllr Morris Bright said tattooists operating under the radar posed "a real danger" to people's health as they often have low hygiene standards which "could put your life at risk".
"They can use unsterilised equipment that seriously increases the risk of spreading diseases such as hepatitis or HIV and causing permanent, ugly scarring," he said.
"Unregulated tattooists are also associated with bad tattoos, which require expensive work to put right, and because they've been done illegally, you won't have normal customers' rights.
"We would also encourage anyone who has visited an unregistered tattooist to seek medical advice from their GP and report the parlour to their local authority."
Council environmental health teams are in charge of carrying out raids and prosecuting illegal tattooists.
Those who ignore the law can also be prosecuted under health and safety legislation, which can lead to a £20,000 fine or a jail sentence.
In September 2015, Wrexham County Borough Council prosecuted a man for illegally tattooing children in his home for "pocket money prices".
He was fined just over £600 for six offences and a court order was issued for the destruction of his tattooing equipment.
About 20% of British adults have had a tattoo, according to a You Gov survey in 2015.