Cookies are as much of a part of the holidays as wrapped presents and watching “A Charlie Brown Christmas.” But whether you're baking from scratch or using ready-to-bake dough, resist the urge to eat the raw dough.

It used to be that people only worried that the raw eggs in the batter could transmit salmonella, but now there's even more concern about the flour in the dough. Raw flour may contain specific kinds of E. coli that cause disease by making toxin called Shiga toxin. The bacteria are called Shiga toxin-producing E.coli or STEC.

Researchers found 56 cases in 24 states of STEC linked to contaminated flour from December 2015 to September 2016. They had symptoms including vomiting and dehydration. They published their findings in the November 2017 New England Journal of Medicine.

“Flour is derived from a grain that comes directly from the field and typically is not treated to kill bacteria,” says Leslie Smoot, Ph.D., a senior advisor in FDA’s Office of Food Safety and a specialist in the microbiological safety of processed foods, in a press release from June 2016.

If an animal relieves itself in a field, bacteria from its waste could contaminate the grain, which is then harvested and milled into flour. Because flour goes directly from this point into your batter without any sterilization step in between, that's why there's the possibility of getting sick.

This isn't the first time people have been warned about eating raw cookie batter.

In 2009, Nestlé recalled raw cookie dough after people in several states became ill from E. coli O157:H7 infections after eating the dough raw. The Centers for Disease Control and Prevention released a report it conducted about the outbreak. Scientists were never able to pinpoint exactly which ingredient in the raw cookie dough contained the E. coli, but they have a suspicion.

To stay safe when cooking and baking, the CDC offers these tips:

  • Don't taste, eat or let children play with raw dough or batter made with flour, whether for cookies, tortillas, pizza, biscuits, pancakes or even crafts.
  • Follow the recipe or package directions for baking or cooking at the proper temperature for the specified time.
  • Don't make milkshakes with products that contain raw flour, such as cake mix.
  • Don't use raw, homemade cookie dough in ice cream. (Cookie dough ice cream sold in stores contains dough that has been treated to kill harmful bacteria.)
  • Keep flour and eggs separate from ready-to-eat foods. Flour can easily spread to other items.
  • Clean up thoroughly after handling flour, raw eggs or dough. Wash your hands well.

Editor's note: This story has been updated since it was originally published in December 2011.

Robin Shreeves ( @rshreeves ) focuses on food from a family perspective from her home base in New Jersey.

Getting ready to bake cookies? Don't eat the raw dough
Tempting as it may be to sneak a taste of raw, ready-to-bake cookie dough, scientific evidence says it's healthier to resist temptation.