Why did women’s rush into the workforce stop? Policymakers have been vexed by the question for years. Social scientists have discussed the sudden stop for over a decade, in conferences and academic papers. Almost 12 years ago, I gave the topic a shot in the pages of The New York Times: why, after a five-decade rise, did the labor-force participation of women in the prime working years stall around the turn of the century?

After years of sometimes scorching debates, over whether highly educated women were “opting out”; whether the stop was merely temporary; and whether it responded to gender roles at home or labor-market conditions, the analysis seems to have converged on a sort of rough consensus: caring for children — overwhelmingly a woman’s task — ultimately took its toll.

Caring for children is, to be sure, a formidable barrier to women’s work. In developed countries where parental leave is guaranteed by law and governments ensure free child care, women work at a much higher rate than in the United States.

Still, the consensus is incomplete. It misses perhaps the most significant impediment to women’s continued engagement in the labor market, one that is getting tougher with each passing year: aging. Focused laserlike on child care, we haven’t noticed that the United States is walking into an elder-care crisis.

Today almost 15 percent of the U.S. population has reached the official retirement age, according to figures from the United Nations. That is about 2 percentage points higher than at its previous peak in 1995, just a few years before the labor supply of women in the prime working years — 25 to 54 years old — reached a plateau. It means that for every four Americans of working age, there is one of retirement age, the World Bank says.

Lots of these older Americans — 14 million, according to Paul Osterman of the Massachusetts Institute of Technology’s Sloan School of Management — can’t live independently and care for themselves.

The burden of care weighs predominantly on their wives and the daughters. About a quarter of women 45 to 64 years old and one in seven of those 35 to 44 are caring for an older relative, according to the American Time Use Survey.

It takes a toll. Ten percent of caregivers have to cut back on their hours at work; 6 percent leave their jobs entirely, according to a report last year by the National Association of Insurance Commissioners.

A 2015 survey by the insurer Genworth Financial found that caregivers spend about 20 hours a week providing care — about half what a full-time worker would spend at work. Almost four in five said they had missed work, and about one in 10 lost a job. One in six reported losing around one-third of income because of caring responsibilities.

Sean Fahle of the State University of New York at Buffalo and Kathleen McGarry of the University of California, Los Angeles, tracked women in their early 50s to their early 60s for 20 years. Those who provided care, they found, were 8 percent less likely to work. Those at work cut their hours and had lower wage growth. Over time, McGarry told me, caregivers risked lower incomes and a higher risk of poverty in old age.

The stress is getting no lighter. By 2030, more than 1 in 5 Americans will have reached retirement age. That will call for a lot of caregiving. One study found that retired members of the baby boom generation will need, on average, three years of long-term care. One in five will need more than five years of care.

This is expensive. Older Americans may be healthier than ever. Still, as they age, they will inevitably develop disabilities and chronic conditions like dementia.

“If you are superwealthy and can afford all sorts of things, this is not an issue,” noted Lawrence F. Katz, a professor of economics at Harvard. “But if you are middle class, this tends to end with your relatives’ losing all of their assets and relying on Medicaid or family care.”

There is a broader societal challenge: how to fit a social safety net built in the 1930s, when wives stayed at home and life expectancy was 20 years shorter, into a world in which husbands and wives must juggle work with the demand for care from their elders and their children.

It is probably naïve to harbor these thoughts just as Republicans in Congress and the White House are engineering a tax cut for corporations and wealthy Americans that will reduce government revenue by $1 trillion over a decade. It may sound crazy to say this just as Republican leaders are turning their sights on the next step of the strategy: cutting spending on programs like Medicaid and Medicare to pay for the tax effort. But perhaps this is time to beef up the safety net to incorporate the rising demand for care.

In his book “Who Will Care for Us?,” published this year, Osterman estimates that there are about 21 million family members caring for an adult relative for no pay. By 2040, he predicts demand for such care will rise to 34 million.

Ai-Jen Poo, co-director of Caring Across Generations, a coalition of advocacy groups pushing for an expansion of public insurance to incorporate universal care, notes that private insurers are not the solution: They can’t cobble together a big enough risk pool to cover the enormous cost of care for everyone.

“All the insurance companies are trying to get out of that market,” she said. “This is a problem that the market can’t solve.”

With little hope for action at the federal level, Poo is putting her hope on states. A bill providing for universal long-term care has been introduced in the Washington Legislature. Caring Across Generations has had some success in pushing for adding government subsidies to care in Hawaii. It is backing a referendum on a universal care program in Maine. But without some public intervention, she said, “there will be a humanitarian crisis, both for the aging and the workers that care for them.”

And if prime-age women start leaving the workforce in even higher numbers to care for their aging parents, this will also be a problem for the U.S. economy.

© 2017 The New York Times Company