Why Do Eggs Get Salmonella?

Whenever you're tempted to indulge in a spoonful of raw cookie dough, that little voice in your head reminds you that cookie dough contains raw eggs and there's a chance you could get salmonella. You might do it anyway, but that's because you likely know the risk is extremely low. If it's so rare for an egg to be contaminated with salmonella, then how do eggs get it in the first place?

There are a few ways that eggs could pick up salmonella. In one possible instance, there is a window of time between when the egg forms inside the chicken and when the shell forms. During this time, it's possible for the egg to pick up salmonella. Salmonella can also get on the shell of an egg while it's being hatched or afterward, since the chicken expels eggs from the same place it excretes feces. Salmonella can transfer from chicken droppings that the egg touches as it hits the ground. In the U.S., eggs are washed before reaching grocery store shelves to kill any bacteria on the exterior of the eggs. But other countries, like the U.K., instead vaccinate their chickens against salmonella, which is why British eggs don't need to be refrigerated and are safe to consume raw.

Children in the U.S. learn from a young age not to eat raw eggs — and in the name of food safety, that remains true. However, the chances of getting salmonella from an egg are actually quite slim; the Center for Disease Control and Prevention estimates that only about one in 20,000 eggs carries the bacteria (per Live Science). The best way to avoid salmonella is by cooking eggs thoroughly before consuming them, but there are other steps you can take to help lessen that risk, too.

Make sure you always keep your eggs refrigerated, and only buy them from grocers or farmers who refrigerate them. Grocery store eggs generally have a lower risk of salmonella than farm-fresh eggs because commercial eggs' exteriors are usually sanitized before they're packaged and sold; if they're not, don't try to wash the eggs yourself. If you find a cracked egg in the box, it's best to discard it because salmonella from the shell can make its way into the cracked egg.

If you're using raw eggs for any dish that requires them, such as Hollandaise sauce or homemade cookie dough ice cream, try to find pasteurized eggs instead of fresh eggs. Pasteurized eggs have a similar texture to regular eggs but are safe to eat raw because they have been heated to kill bacteria.