With retail spending on the rise, what's keeping the U.S. consumer going?

News of the war in Iran didn’t seem to keep consumers from spending last month. Retail sales in March were up 1.7% from February and up 4% compared to a year ago.

The uptick is some of the latest evidence of consumer resilience, but there are a few signs of strain starting to show.

There’s one thing to keep in mind about the strong sales numbers in March, said Rick Miller of Big Chalk Analytics.

“Retail spending numbers are how much money consumers spent on stuff, not how much stuff they got,” Miller said.

The more than 15% jump in spending at gas stations isn’t because everyone splurged on a weekend road trip. But even when you strip out volatile spending on gas and car parts, retail sales still rose 0.6% from the month before. Some of that is thanks to big tax refunds, said Jessica Ramírez, co-founder of consumer insights and retail strategy firm The Consumer Collective. But people are also taking on more debt in order to keep spending.

“We’ve seen buy now, pay later increase. We’ve seen credit card debt increase,” Ramírez said.

Taking on debt can mean consumers see better days ahead. But LendingTree’s Matt Schulz said there are some red flags.

“About 30% of buy now, pay later users are using those loans for groceries. That certainly doesn’t seem like a sign of the healthiest consumer,” Schulz said.

He said that, just two years ago, buy now, pay later was more often used on discretionary items like handbags and gaming consoles.

Perhaps the biggest reason people are still spending though, is the labor market, said Craig Rowley of Korn Ferry.

“Unemployment's still in the 4% category, which historically is not high,” Rowley said.

He said that’s a number to watch if you want to know where consumer spending could go in the future.