(Bloomberg) -- If you’re hearing a cry go up across the land, it may because of the latest shortage building in the U.S.:  baby formula.

Six states were showing out-of-stock percentages for baby formula higher than 50% for the week starting April 24, with the number of states nearing 50% more than tripling to 26 from just three weeks earlier, Datasembly said in a statement provided to Bloomberg. Nationwide the average was 40%, building from 31% in early April and 11% at the end of November.

Shortages of formula began to take effect last summer amid supply chain disruptions, product recalls and inflation. Some retailers have  responded with rationing. Purchases are being capped at some chains, including CVS Health Corp. stores.

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

There also are limits of three per customer at Walgreens stores and four per customer at Target, according to CNN. Target and Walgreens didn't couldn’t be reached for comment.

Florida pediatrician Mona Amin said some of her patients are struggling to find the formulas they normally use, and that switching brands raises a different set of issues.

“There are alternatives you can take, but the problem is that it's not always such a simple switch,” Amin said. Babies with health conditions may need specialized formula, and some children may have gas, discomfort or spit up when using a different brand.

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