Last year, people in the U.S. made an estimated $4.7 billion selling about 62.5 million liters of their plasma, a more than 30% increase in the amount of plasma collected since 2022, according to Peter Jaworski, a professor at Georgetown University who studies the ethics and economics of the plasma business. The transactions occur in more than 1,200 plasma centers " there are now more places to sell plasma than there are Costco stores " and more are popping up in solidly middle-class neighborhoods, including suburban strip malls and college towns, Jaworski said. As America's economic divide widens, with the top 1% of households owning more than 30% of the country's wealth, the payments people receive for selling plasma are playing a quiet role in keeping households above water financially.