Major retailers in the US have begun rationing baby formula amid soaring out-of-stock rates, according to media reports on Sunday.

Some pharmacies and supermarkets are limiting shoppers to three infant and toddler formula products per purchase in stores and online, USA Today says, quoting the retailers.

“Due to increased demand and various supplier challenges, infant and toddler formulas are seeing constraint across the country,” the publication quotes Walgreens Boots Alliance spokesman Steve Cohen as saying.

Between November and April, the out-of-stock rate for baby formula – a manufactured breast milk substitute made mostly from cow milk – jumped from single digits to nearly 40% nationwide and even exceeded 50% in some states, according to the latest figures from market data analysis company Datasembly.

Finding formula has become a challenge for parents, CNN says, describing how some have to drive to neighboring states or go on social media and plead with strangers to share or even barter any extra supply they may have. One mother told USA Today that “it’s almost a full-time job trying to find Similac {a brand of infant formula}.”

“Inflation, supply chain shortages, and product recalls have brought an unprecedented amount of volatility for baby formula,” said Datasembly CEO Ben Reich, warning that there’s “no indication of a slowdown.”

According to CNN, manufacturers are producing at full capacity but it’s still not enough to meet current demand. The shortage has been exacerbated by a recall in February of three brands of powdered baby formulas due to concerns about bacterial infections and a shutdown of a major factory.

The birth rate in the US has been climbing steadily in recent years, while inflation has soared over the past year at its fastest pace in more than 40 years.