One Direction apparently see tattoos as a way to "assert themselves as men".
Harry Styles has the most inkings in the group, notching up 42 since he first went under the needle last year. Zayn Malik has 24, with his newest addition a likeness of his girlfriend Perrie Edwards.
Louis Tomlinson and Liam Payne also have body markings, although Niall Horan has yet to colour his skin.
The four singers with inkings apparently hope they make them look grown up.
"The boys started having them done to assert themselves as men, rather than the boys who were in The X Factor," an insider told British magazine Heat. "They're so controlled in every aspect of their lives it's also their way of rebelling."
There is said to be an element of competition between the boys too.
Harry and Zayn apparently vie to see who can get the most designs, although all four of the stars are adamant they have tattoos for the right reasons.
"Harry says it's about permanently signifying his journey, because he knows it won't last forever," the source explained. "Zayn has his X Factor number, six, on his forearm, and Louis and Liam also have symbols and sayings that mean things to them."
Other stars have started to notice the five-piece band's love of inkings. Robbie Williams recently poked fun at the lads, joking he was in the "One Direction bad tattoo club". "They've got some horrendous ones," he laughed.