Fido’s friskiness means male dogs are more likely than females to get a certain type of cancer.

Canine transmissible venereal tumors, or CTVT, are spread between dogs by skin contact, as cancer cells “stick” to the new dog, according to a study by University of Cambridge researchers that was recently published in the journal Vet Record.

The contact happens through mating, but also through butt and crotch sniffing and licking — activities male dogs do more often than female, Newsweek reported.

Although cases of genital CTVT are equal among males and females, males are four to five times more likely to get the oronasal version of the cancer, which affects the nose and mouth, according to the research.

“Male dogs sniff vaginal secretion odor more frequently than female dogs,” the authors said in the paper. “Furthermore, female genital CTVT tumors tend to be more exposed and accessible for licking or sniffing than those of males.”

Out of 2,000 cases, 32 were the oronasal version and 27 of them occurred in male dogs, according to the research.

Although more common in males, contracting a CTVT tumor through licking is still uncommon overall. 

“The rarity of oronasal CTVT in the population, despite the likelihood that opportunities for licking and sniffing transmission behavior arise frequently, suggests that transmission of CTVT by sniffing or licking is an unlikely outcome,” the authors said.

The disease can also be contracted through smelling other dogs’ anal glands, which helps them determine if they had previously met.

CTVT date back to one dog who contracted the cancer 11,000 years ago, and it then spread like wildfire. It is most commonly found among free-roaming and stray dogs, according to Newsweek.