A cheeseburger and french fries, a classic American lunch, but researchers found it may come with an extra dose of phthalates, a chemical linked to disease including cancer.
Phthalates are used to make food packaging, processing equipment and takeout boxes and may be seeping into food, according to research from George Washington University.
They found levels of the chemical were 35 percent high in people who regularly ate at restaurants, cafeterias and fast food joints.
Teenagers were the most likely to have higher levels in their body.
"When people are eating out all the time time and eating packaged foods and eating at fast food restaurants, you're going to be exposed to more," said registered dietitian Jennifer Neily, who doesn't think the findings should cause people to overreact.
However, she says, they should prompt most people to re-think their eating habits, such as preparing their own food at home.