Health officials are lending legitimacy to the age-old warning not to eat raw cookie dough.

The Food and Drug Administration issued a warning on Tuesday about a recent E. coli outbreak linked to contaminated flour, advising consumers not to eat raw dough — including that for bread, pizza and cookies.

The FDA is investigating the outbreak with the Centers for Disease Control and Prevention, which reported on June 1 that 38 people in 20 states had been infected with Shiga toxin-producing E. coli O121. No deaths have been reported, but 10 people have been hospitalized.

Flour produced at a General Mills facility in Kansas City, Missouri is a likely source of the outbreak, the CDC said. The company recalled several varieties of flour in May.

“For the most part, the risk from flour is pretty low, and most use of flour involves a ‘kill step’ — people bake with it,” said Jenny Scott, a senior adviser in the F.D.A.’s Center for Food Safety and Applied Nutrition, the New York Times reported. Before it is baked, flour is typically not treated to kill bacteria.

The FDA advises people not to eat cookie dough, cake batter or any other raw dough, and to wash hands and utensils thoroughly after cooking.

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Write to Katie Reilly at Katie.Reilly@time.com.