The One Direction singer is said to allow his friend to use a home tattoo kit in order to create his latest body art, according to The Sun.
Using such kits reportedly bring risks of hepatitis, TB and other infectious diseases.
However, the 18-year-old's regular professional tattooist has told Styles to stop the home methods.
Kevin Paul, 34, of Derby, said: "I tried to explain to him what the risks were but he doesn't seem to care."
[Two of Harry Styles's recent tattoos]
Paul is also known to provide tattoos for stars including James Arthur and Ed Sheeran, among others.
Styles recently showed off a new ship tattoo on his arm with his rumoured girlfriend Taylor Swift.
The teenager was alleged to have broken up with Swift because she "didn't want to put out".
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