“I really started to panic,” she told Fortune.

Over the next two weeks, Schmier says she spent all her free time driving from store to store, looking for Similac Pro-Sensitive, the specific formula that works best for her son. She says she’s hesitant to switch brands because of how he’s reacted to changes in the past.

“Striking out most of the time, but when I could find formula I just purchased it,” says Schmier, who is the vice president of government relations at MomsRising, a nonprofit focused on issues facing women, mothers, and families.

But the baby formula problem hasn’t gotten any better since then. She hasn’t been able to buy the formula in a store for about a month, and her current stockpile is running out. 

Schmier is one of countless parents hit hard by the current baby formula shortage in the U.S., which experts say has reached unprecedented levels and has been building since mid-2021. The shortage is the result of combined supply-chain issues and a recent recall by Abbott Nutrition, which owns several baby formula brands, according to the Infant Nutrition Council of America, an association of formula manufacturers.

Abbott Nutrition’s product recall came after four children fell ill and two died after consuming powdered formula produced in one Michigan facility, according to the U.S. Food and Drug Administration. 

“We are doing everything we can to address the infant formula supply shortage,” said Abbott in a statement to Fortune. “Across the U.S., we’re prioritizing production of infant formula products to help replenish the supply in the market and are also air shipping in product from our FDA-registered facility in Cootehill, Ireland, on a daily basis. All of this powder product is being restocked on retail shelves on a regular basis.”

Baby formula stock was relatively stable for the first seven months of last year, with an out-of-stock rate hovering between 2% and 8%, according to Datasembly, a provider of real-time product pricing, promotions, and assortment data for retailers and consumer packaged goods (CPG) brands.

But that all changed in November 2021, when the out-of-stock rate for baby formula, both powder and liquid varieties, started to increase, hitting  31% in early April. It has continued to rise since then; the out-of-stock rate hit 40% for the week starting April 24, the most recent data available, according to Datasembly, which surveyed over 11,000 stores across the country. 

To supplement the formula she has on hand, Schmier says she’s relied on an informal support community of mothers to supply her with cans they don’t need anymore. “It’s a nightmare,” she says. “What I was able to cobble together in that two-week period at the beginning of March is what I have now. 

“I look all the time,” says Schmier. “I’ve looked online, I have my mom in Boston looking, my mother-in-law in Florida looking. Everyone we know is looking for us and no one can find it.”

As of April 24, six states have out-of-stock rates higher than 50%: Iowa, South Dakota, North Dakota, Missouri, Texas, and Tennessee. Three weeks ago, only seven states were suffering an out-of-stock rate exceeding 40%. Now there are 26, according to Datasembly.

As a result, major suppliers and retail chains including CVS, Target, and Walgreens have begun to limit the number of cans of powdered baby formula that customers can buy at once. 

“Following supplier challenges and increased customer demand, we currently have a limit of three baby formula products per purchase in our stores and online,” CVS said in a statement to Fortune. “We’re continuing to work with our baby formula vendors to address this issue, and we regret any inconvenience this causes our customers.” 

In a statement to Fortune, Target confirmed to Fortune it was limiting baby formula purchases to four units per customer for online purchases, but there is no limit to in-store purchases.

Walgreens did not immediately respond to Fortune’s request for comment.

Schmier says she hasn’t seen three cans of the kind of formula she needs in a single place. “That would be a luxury,” she says.

Working-class families are likely to suffer the most from the shortage. 

“As inflation soars, food and gas prices are skyrocketing,” says Caron Gremont, director of early childhood for Share Our Strength’s No Kid Hungry campaign, adding that “millions of families already struggling are going to be pushed off of a hunger cliff.”

All infants, however, face health risks if their parents are not able to secure proper formula.

“Unlike other food recalls, shortages in the infant formula supply affect a major—or even exclusive—source of nutrition for babies,” said Brian Dittmeier, senior director of public policy at the National WIC Association (NWA), the USDA’s supplemental nutrition program for low-income families, said in a statement to Fortune. “Inadequate nutrition could have long-term health implications for babies.”

More than 1.2 million infants receive formula benefits through WIC, according to Dittmeier, who added that Abbott is the exclusive supplier for more than half of the program’s agencies in the U.S. 

The shortage could be most serious for parents whose children suffer from medical issues that preclude them from easily changing formulas. It’s also particularly tough on caregivers in rural communities who might rely on a single drugstore half an hour away from home to buy formula, and don’t have the privilege of shopping different stores in a city. 

Schmier worries that parents might be pressured to take a dangerous course of action in the face of continued baby formula shortage. Without their regular formula easily accessible, she says parents might unknowingly put their kids at risk by using recalled formula, turning to homemade recipes, using cow’s milk too early, or watering down formula and making it less nutritious. 

“There’s a risk of people being desperate and unknowingly doing things that could be unsafe for their child,” she says.