06/15/2015 09:24 am ET | Updated Jun 15, 2015

Here's How Much Mouse Poop The FDA Allows In Your Food

YOSHIKAZU TSUNO via Getty Images

You've probably eaten mouse poop -- and the federal government is just fine with that. It's also fine with mold, rat hairs and insect legs.

The Food and Drug Administration, you see, has detailed guidelines on how much filth can be found in many of the foods sold in America. The FDA enumerates these guidelines in a document known as the "Defect Levels Handbook." The introduction to the handbook explains that "it is economically impractical to grow, harvest, or process raw products that are totally free of non-hazardous, naturally occurring, unavoidable defects" -- and that these so-called "defects" present no real risk to human health.

The FDA also says that many food companies take measures to ensure that their food actually contains far lower levels of these defects than their regulations require. If a food exceeds these levels, the FDA can label it "adulterated" and ask that it be taken off store shelves.

That all makes total sense, of course -- accidents happen, especially when food is produced at an industrial scale. But the Defects Levels Handbook nonetheless makes for some grisly reading. You probably already know and accept, at least on some dim level, that when you're eating delicious foods, you're also ingesting minute quantities of unrelated animal products. But to see it all spelled out is just gross.

The yuckiest of the defects is surely what the handbook calls "mammalian excreta." Not only is poop inherently disgusting, mouse droppings can spread the lethal (if exceedingly rare) Hantavirus.

The amount of excrement permitted varies from food to food. Many spices and herbs, including pepper, thyme, hot peppers, cinnamon bark and oregano, have a limit of 1 mg of excrement per pound of food. There are over 450,000 milligrams in a pound, so that's a very small fraction. Some whole spices, such as fennel seeds, ginger and mace, have a slightly higher limit of 3 mg per pound. The highest limits are on cocoa beans (10 mg per pound) and wheat (9 mg per kilogram).

The handbook also specifies acceptable limits for other potential adulterants like mold, rot, rodent hairs, insect parts and insect larvae. These, too, vary wildly. Black currant, for example, can have a "mold count" -- which refers to the percentage of samples showing any traces of fungi under a microscope -- as high as 75 percent, while pineapple juice can't exceed 15 percent.

The insect limits sound rather high to the untrained ear: 925 insect fragments are allowed in just 10 grams of ground thyme, for instance, while 100 grams of canned asparagus may include 40 thrips, a kind of tiny winged insect. The best thing to do is probably to just think of it as protein. Heck, people spend hard-earned money on cricket flour -- so why what's the harm in getting 75 insect fragments free with each 50 grams of wheat flour you buy?