The memos were concise and direct.

An executive at Johnson & Johnson said the main ingredient in its best-selling baby powder could potentially be contaminated by asbestos, the dangerous mineral that can cause cancer. He recommended to senior staff in 1971 that the company “upgrade” its quality control of talc.

Two years later, another executive raised a red flag, saying the company should no longer assume that its talc mines were asbestos-free. The powder, he said, sometimes contained materials that “might be classified as asbestos fiber.”

The carcinogen, which often appears underground near talc, has been a concern inside the company for decades. In hundreds of pages of memos, executives worried about a potential government ban of talc, the safety of the product and a public backlash over Johnson’s Baby Powder, a brand built on a reputation for trustworthiness and health.

Executives proposed new testing procedures or replacing talc outright, while trying to discredit research suggesting that the powder could be contaminated with asbestos, according to corporate documents unearthed by litigation, government records obtained by The New York Times through the Freedom of Information Act, and interviews with scientists and lawyers.

In one instance, Johnson & Johnson demanded that the government block unfavorable findings from being made public. An executive ultimately won assurances from an official at the Food and Drug Administration that the findings would be issued only “over my dead body,” a memo summarizing the meeting said.

Those efforts are now forming the crux of a new legal front in a long-running battle over Johnson’s Baby Powder, potentially leaving the company exposed in nearly 12,000 lawsuits across the country claiming that the product can cause cancer.

This summer, 22 women with ovarian cancer successfully sued the company, arguing that Johnson & Johnson knew about the connection between talc and asbestos. A jury in St. Louis awarded them $4.69 billion, one of the largest personal injury verdicts ever.

The company lost two other cases this year, in California and New Jersey, brought by people with mesothelioma, a cancer of the lining of internal organs that is associated with asbestos.

The prospect of asbestos “puts the defense in a much more difficult position,” said Nathan Schachtman, a lawyer who has defended asbestos companies. “You get a much higher degree of indignation from juries.”

Shares of Johnson & Johnson dropped 10 percent on Friday on an article by Reuters about the asbestos concerns related to Johnson’s Baby Powder.

Johnson & Johnson is appealing the three asbestos-related cases. The company has won three cases related to mesothelioma, while four others were declared mistrials.

The company defends the safety of its baby powder, saying that it has never contained asbestos and that the claims are based on “junk science.” Johnson & Johnson says that the lawyers in the cases have “cherry-picked” the memos, and that they instead show the company’s focus on safety.

“Johnson & Johnson’s talc has been tested by scientists at multiple entities since the early 1970s up to the present,” said Peter Bicks, a partner at Orrick, one of the law firms representing the company in the lawsuits. “None of these routine tests over the past 50 years detected the presence of asbestos.”

For more than a century, Johnson & Johnson has promoted its baby powder as pure and gentle enough for babies’ bottoms, a product that mothers can trust, made by a company that puts customers first.

The company’s image has long been bound up in the product and its iconic white bottle, even though baby powder counts for only a sliver of overall sales. Its fragrance is said to be among the most recognizable in the world. Employees have called it a “sacred cow” in emails, according to court documents.


Krystal Kim, who has been treated for ovarian cancer, was one of 22 women who won a lawsuit against Johnson & Johnson in St. Louis in July.CreditMichelle Gustafson for The New York Times

Krystal Kim, a 53-year-old mother of two from Philadelphia, was 10 when her mother suggested she use Johnson’s Baby Powder to stay “fresh” and “clean smelling.” She continued using it for decades, on her face, between her legs and on her sheets. Many women use baby powder as a feminine hygiene product, applying it to their bodies and breathing in airborne powder.

Five years ago, Ms. Kim learned she had invasive ovarian cancer and was treated with chemotherapy. Parts of her colon and intestines were removed. Ms. Kim, one of the plaintiffs in the Missouri case, wants Johnson’s Baby Powder taken off the shelves and, if not, warnings put on it.

Before the Missouri verdict, Johnson & Johnson had been able to knock back most of the legal challenges that connected talcum powder alone to cancer, by claiming, in part, that the scientific research was flawed and offering studies to the contrary.

Of the six cases that Johnson & Johnson has lost on that issue by itself, three decisions were overturned on appeal, one is still being appealed, and one plaintiff won her case but was awarded no damages. One verdict, for $110 million, has been upheld by a judge; the company is appealing.

But asbestos, unlike talc, is an indisputable carcinogen. Even trace amounts are considered dangerous. Its dagger-like fibers penetrate deep into tissue and can lead decades later to cancer of the lungs, voice box and ovaries, and to mesothelioma.

Several lab tests, some conducted in the past few years by plaintiffs’ lawyers, have found evidence of asbestos in talc. The link between asbestos and ovarian cancer was first reported in 1958, and in 2011, the International Agency for Research on Cancer said it was a cause.

“There’s no ambiguity,” said Mark Lanier, the lawyer who represented the women in the Missouri case. Mr. Lanier has won large industry payouts for workers who were exposed to asbestos on the job.

“It’s a no-brainer that asbestos causes ovarian cancer,” he added. “That’s not an argument anyone will win.”

Asbestos was once ubiquitous in home insulation, shipyards, factories and even automobile parts. It was cheap to mine, durable and strong.

By the early 1970s, it was also widely considered dangerous. As consumer groups sounded the alarm, environmental scientists started testing building materials and household products that might contain asbestos.

Two mineralogists, Arthur Langer at Mount Sinai Medical Center and Fred Pooley of University College Cardiff in Wales, collaborated on a study about the asbestos content of powders sold on both sides of the Atlantic. Mr. Pooley planned to present their findings at an occupational health conference in Britain in September 1975.

But he had also been a consultant for the cosmetics industry. When Mr. Langer revealed that he had found minerals that might be asbestos in Johnson’s Baby Powder, Mr. Pooley called to warn the company.

Johnson & Johnson executives slammed Mr. Langer in internal memos as “devious,” saying his data was “controversial.” Mr. Pooley canceled his presentation, and the company pressured him to pull the report from the conference materials.

Mr. Pooley could not be reached for comment.

Mr. Langer continued the research without Mr. Pooley. And in 1976, he and colleagues at Mount Sinai told reporters that they had detected asbestos in several commercial talcum powders, though they explicitly said it hadn’t been found in Johnson & Johnson’s products. The results were later published in a journal.

The company went on the offensive anyway. Within days, executives met with Mr. Langer and two of his colleagues and said they should avoid “frightening mothers unnecessarily,” according to a company memo describing the meeting.

“It was pointed out in plain language to the Mt. Sinai group that appropriate correction of their statements should be made to the news media and the public, and that this should be made available by noon of the next day,” the memo said.

In response, the Mount Sinai scientists told the company that they actually had found asbestos in Johnson & Johnson’s talc but hadn’t mentioned it because they thought the levels were too low to be of significance.

Eight days later, Dr. Thomas C. Chalmers, Mount Sinai’s president, issued a news release to correct “misimpressions the media reports may have generated” about talc. He said that the asbestos tests had been run on older powders, that new ones were safe and that Mount Sinai’s pediatricians endorsed using baby powder on babies.

But one of Mr. Langer’s colleagues from Mount Sinai disputed Dr. Chalmers’s statement in a 1976 interview with The Washington Post, saying the team had tested new and old powders. The newspaper also quoted a Food and Drug Administration official saying that Mount Sinai’s testing methods could detect asbestos at lower levels than the agency could.

Mount Sinai received funds throughout the 1970s from the Robert Wood Johnson Foundation, according to the foundation’s annual reports. The foundation, which was established as a national philanthropy in the early 1970s with $1.2 billion in Johnson & Johnson stock, is independent from the company. But during the 1970s, several senior executives, including the chief executive Philip B. Hofmann, served on the foundation’s board. Others joined the board after retiring from the company.

Mr. Bicks, Johnson & Johnson’s lawyer, said the company had never influenced the foundation’s decisions.

Dr. Chalmers died in 1995, and a Mount Sinai spokeswoman said she could not comment on events from so long ago. The medical center’s press office denied a request to see its archives.

In a recent interview, Mr. Langer told The Times that Dr. Chalmers “spoke for himself and for the institution, not our research group.” He reiterated that his team had detected asbestos in Johnson’s Baby Powder.

“I stand by that today, absolutely,” he said.

With the increasing concern over asbestos, the Food and Drug Administration was under pressure to regulate talc, which is also used in makeup like mascara, lipstick and face powder. In the early 1970s, the agency commissioned Seymour Lewin, a well-regarded chemist at New York University, to test talc products. Mr. Lewin found asbestos in more than half the 11 Johnson’s Baby Powder samples he tested.

An industry trade group was given a confidential copy of the report by the F.D.A. The group, which shared it with Johnson & Johnson, threatened to sue to try to block it from being made public.

The company asked the F.D.A. to hold the findings in “strict confidence,” according to a memo summarizing a meeting. “A release of such untrue information will create a great deal of unwarranted alarm,” executives told the F.D.A.

An agency official told the company that the report would be issued only “over my dead body,” according to an internal corporate memo about the conversation.

Johnson & Johnson asked Walter McCrone, the scientist who usually tested its talc, to visit Mr. Lewin and inspect his slides. The company also compiled testimonials and data from other scientists to challenge Mr. Lewin’s results.

The final report by Mr. Lewin looked different. Though he had initially said the tainted Johnson & Johnson’s talc samples contained 2 percent or more of asbestos, the final version sent to the F.D.A. said that most were free of asbestos and that two test results were inconclusive.

Ultimately, the government retreated from a plan to regulate asbestos in talc. The cosmetics trade group adopted a standard of “zero tolerance” for asbestos in talc, but adherence is voluntary.

“The F.D.A. takes the possible presence of asbestos in cosmetics very seriously, and the agency uses several means to monitor cosmetic safety generally, including conducting research, to help ensure that cosmetics available to American consumers are safe,” the agency said in a statement.

It said that the most recent tests of cosmetics, in 2009-10, had found no asbestos, but that the results were “limited” since few products and raw talc samples had been tested.

“The F.D.A. also continues to investigate and monitor reports of asbestos contamination in certain cosmetic products, and will provide additional information as it becomes available,” the agency added.

Mr. Lewin died several years ago. But Aviam Elkies, who was a doctoral candidate and testified that Johnson & Johnson had funded him to work in Mr. Lewin’s lab in 1972 analyzing samples from talc mines supplying the company, said he and Mr. Lewin had detected asbestos in at least half the samples they tested.

“It appeared randomly in samples taken from the same mines,” Mr. Elkies said in an interview in Israel, where he lives. “It appeared in different concentrations. There was no pattern, no way to predict.”

He said Johnson & Johnson had terminated the project after learning about the results and yanked his scholarship money. Mr. Elkies did not finish his degree and moved to Israel, where he taught chemistry to high school and college students.

Mr. Bicks said that Johnson & Johnson was not aware of any evidence that Mr. Elkies had a scholarship from the company and that Mr. Elkies reported testing talc from mines in Canada and New York that the company didn’t use.

Johnson & Johnson’s efforts to temper the debate over its baby powder continue today. It has sought to have documents used in court sealed, hired lawyers known for their work in crisis management and created a website to extol talc’s safety.

The website, started in 2016, initially mentioned asbestos once. It now mentions asbestos several times in sections about safety and mesothelioma.

“When science is false and inaccurate, it should be corrected,” Mr. Bicks said.

Darlene Coker developed mesothelioma in 1997. But Ms. Coker, then 52 and living in Beaumont, Tex., had never worked in shipyards, construction or mining, like many mesothelioma sufferers. She was a lifelong user of Johnson’s Baby Powder.

When she sued Johnson & Johnson, she didn’t get far. As part of the discovery process, her lawyers tried to get information about asbestos from the company. Its response: There wasn’t anything relevant.

When they asked for names of labs that had tested Johnson’s talc for asbestos and records of the test results, Johnson & Johnson told them that the questions were “vague.” Requests for documents were declined for being “over broad and unintelligible,” according to legal filings. The company called it a “fishing expedition.”

Ms. Coker’s lawyers withdrew the case. She died in 2009 from mesothelioma.

Mr. Lanier, the lawyer in the Missouri case, said he planned to revisit Ms. Coker’s lawsuit now that the documents obtained in recent cases showed that the company did have information to share.

Mark Lanier, a lawyer who represented the plaintiffs in Missouri, said he planned to revisit an older case in light of company documents that recent cases have revealed.CreditTodd Spoth for The New York Times

The recent spate of asbestos-related cases, which has unearthed the troves of internal Johnson & Johnson’s documents, is prompting a broad legal rethink by plaintiffs’ lawyers.

After the Missouri trial, Michael J. Miller, a lawyer in Virginia involved in the talc litigation, said more plaintiffs lawyers were considering whether their clients’ ovarian cancer was linked to asbestos.

“We knew for years that there was something about the talc that caused ovarian cancer, and there had been rumors about asbestos, but we were really being stonewalled by Johnson & Johnson about the documents we needed,” he said. “The trial in St. Louis was very instructive, very informative, and it’s got us all enthused.”

Mr. Miller’s firm represents 900 plaintiffs who have blamed their ovarian cancer on long-term use of Johnson’s Baby Powder. He expects his first trial in early 2020.

“We didn’t even need to know there was asbestos in there to win these cases, but now that we know, it makes it even easier,” he said. “We’re all eager to get to trial.”