A surge in food prices is deepening the pain caused by Covid-19 across the developing world, forcing millions into hunger and contributing to social problems that could lead to more political unrest and migration. Food prices have jumped by nearly a third over the past year, according to the Food and Agriculture Organization of the United Nations, even as pandemic-related job losses are making it harder for families to afford basic staples. Corn prices are 67% higher than a year ago, the FAO says, while sugar is up nearly 60%, and prices for cooking oil have doubled.

Overall prices have risen for 11 consecutive months to the highest levels since 2014, the FAO says.

Many, though not all, of the causes are linked to Covid-19. Global food supply has largely held up after some initial disruptions last year, experts say.

But pandemic-related restrictions on movement have added to logistical costs. Weaker currencies in many developing countries that are struggling to rebound from Covid-19 have made food imports more expensive—-and conversely, in countries such as Brazil, led to greater exports of food, which are now cheaper for foreign buyers, restricting domestic supply.

And many people who lost income because of the pandemic have eschewed more expensive items like meat and fresh vegetables for staples like wheat that fill stomachs but provide less nutrition, pushing up demand and prices.

“What is unique about this time is that prices are going up, and at the same time people’s incomes have been decimated,” said Arif Husain, chief economist at the United Nations World Food Program. “The combination of the two, rising prices and no purchasing power, is the most lethal thing you could deal with.”

Sonia Regina Dominato, a mother of four in a gang-ridden favela in Rio de Janeiro, had to give up a job as a cook during the pandemic to look after her sick grandmother. With the downturn, her husband hasn’t been able to find much work as a laborer.

“I’m terrified they’re going to get sick,” said Ms. Dominato, whose youngest is a year old. “When I see that there is only enough milk for another day, I can’t sleep.”