The eldest Kardashian daughter, Kourtney, 41, is catching flak for peddling eyebrow-raising claims about the supposed health risks of surgical masks to her 102 million Instagram followers.

On Halloween, the “Keeping Up With the Kardashians” star reposted an unattributed blurb that read in part, “Those Blue Masks Mandated at grocery stores & airplanes are made of PTFE, a carcinogen made of synthetic fluoride.”

The medical warning about PTFE, or polytetrafluoroethylene — a man-made chemical found in nonstick cooking coatings like Teflon — included a picture of a ubiquitous three-ply, single-use blue surgical mask. The post went on: “According to Cancer.Org it increases the risk of liver, testicle, pancreas, kidney & breast tumors + ulcerative colitis, thyroid disease, preeclampsia and high cholesterol. High exposure can cause influenza-like symptoms and hemorrhaging in the lungs, leading to suffocation.”

Kardashian also added her own commentary: a wide-eyed emoji and another with an exploding head. One reader, meanwhile, called her post “scaremongering.”

But the American Cancer Society, listed as the source for the revelations, denounced the advisory.

“There is no evidence to support the claim that the presence of PTFE in a mask causes cancer,” Dr. William Cance, chief medical and scientific officer of the ACS, told The Post.

“As a surgical oncologist, I, along with thousands of colleagues in the health-care profession, have been wearing masks for years to protect patients from the spread of infections,” Cance added.

In fact, an article the ACS published on chemicals found in cookware did not even explore PTFE, but instead warned of another chemical, perfluorooctanoic acid, or PFOA, as having the “potential to be a health concern.”

Plus, there’s no mention of masks in the story. The nose and mouth barriers, which have been proven to help prevent the transmission of coronavirus particles, are not harmful when used properly. The chemicals in question may only be hurtful, and cause the “influenza-like symptoms” mentioned by Kardashian, when an object containing the compounds — such as a Teflon-coated pan — is heated to at least 500 degrees Fahrenheit, breaking down the coating and releasing fumes. In other words, don’t cook and eat your masks.

This is the latest in a series of social-media faux pas from the Kardashian-Jenners in the age of COVID. The clan has been under fire for flying to a private island to celebrate Kim’s 40th birthday — the round-trip travel reportedly set the almost-billionaire back $1 million — with an entourage of 30, and sharing plenty of revealing pics after the fact. Supermodel sister Kendall likewise threw a luxe Halloween-themed birthday bash for her 25th birthday last week in Hollywood, where guests partied unmasked. Momager Kris Jenner told Andy Cohen in a radio interview that all of the guests were tested twice — “We were really responsible,” said the matriarch — even though large gatherings and travel are discouraged due to the pandemic.

Kourtney, who owns the Goop-like lifestyle brand Poosh and is known as the health nut of the family, was recently branded “embarrassing” for modeling “Vote Kanye” merch in apparent support of her brother-in-law, Kanye West. The rapper is running a self-funded, mostly write-in campaign for president. Over the summer, he told Forbes editor Randall Lane that vaccines were ”the mark of the beast.” Flirting with health-related misinformation may be a family sport.

A representative for Kardashian declined to comment when The Post reached out.