Refrigerate your eggs! Here’s why.

Putting eggs in the refrigerator is something I’ve never thought twice about. Sliding the carton into the fridge - the coldest part, please, not the door! - is as reflexive as stashing staples such as milk, meat and leafy greens.

So when a reader submitted a question to our live weekly chat about whether they were wrong to toss eggs that sat out overnight, I stood behind them.

“I bought some Costco eggs and forgot to put them in the fridge. They sat in a cooler chest (no ice) in the kitchen for over twelve hours. I threw them away. My brother said, “Oh they’ll be fine. We leave our eggs out all the time.” I was horrified. It’s not like they’re buying farm eggs where you can maybe get away with that. I told him it was an unsafe practice and he shook me off. Am I off base? Could I have hard boiled them and been okay?”

Readers had a lot to say when I cited the standard government advice about egg refrigeration. Some people told me eggs should “never” be refrigerated, and others offered the (anecdotal) evidence that they had never gotten sick from room-temperature eggs, implying that refrigeration was therefore unnecessary. Still more noted that in other parts of the world, eggs are routinely stored on the counter.

“The refrigeration requirement we have in the United States is based on science,” says Deana Jones, a research food technologist at the U.S. National Poultry Research Center, part of the USDA Agricultural Research Service.

Here’s what you need to know about why it’s best to refrigerate eggs.

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Refrigeration is a matter of food safety

The most common pathogen associated with eggs is salmonella, bacteria often found in chickens’ intestinal tracts, says Amy Johnston, a regional extension educator in food safety at the University of Minnesota. While this may not sicken the hen, the bacteria can be deposited on the eggs as they are laid and then potentially passed on to people; the bacteria can also contaminate the interior of the eggs as they develop, before they are laid. (The European Union has regulations in place regarding vaccinating chickens against one strain of salmonella to help reduce spread and contamination; it is not required in the United States, though some producers do it.)

Some strains of salmonella will more readily infect people than others, but all can cause illness, Jones says. The USDA recommends that eggs at home be refrigerated at 40 degrees Fahrenheit or just below (producers can store and transport them at up to 45 degrees). At warmer temperatures, “you’re putting things in a more positive atmosphere” for bacterial growth, Jones says.

Like any other perishable commodity, eggs are also susceptible to organisms that cause spoilage, Jones says. Refrigeration provides a less hospitable environment for them to thrive as well.

Heating, or reheating, food is not a substitute for proper food storage. While 165 degrees is the temperature at which most pathogenic organisms will be killed, some bacteria may release toxins that are stable to a higher temperature, Jones says. Plus, undercooked eggs, whether intentional or not, are not uncommon, especially in home kitchens where people may not be confirming temperatures with a digital thermometer.

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It’s important to keep previously refrigerated eggs cold

At 45 degrees in the refrigerator, eggs are dry and cold, Johnston says. As soon as they are brought to room temperature, the eggs begin to sweat, and condensation forms on the shells. Among the various factors that can encourage bacterial growth are moisture and warm temperatures, Johnston says, which is exactly what you get when previously refrigerated eggs sit out. Bacteria can as much as double every 20 minutes, and those bacteria may travel from the surface of the shell through its pores into the egg yolk and white.

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Refrigerated eggs maintain quality longer

In 2018, Jones was part of a team that published a study comparing four egg treatment and storage methods: washed and refrigerated at about 39 degrees Fahrenheit; unwashed and refrigerated; unwashed and stored at room temperature, or about 72 degrees; and washed, coated with mineral oil and refrigerated.

“There are drastic differences in how egg quality declined,” when comparing refrigerated to unrefrigerated, Jones says. The study examined the quality of the eggs based on the USDA’s grading standards, with AA considered the highest quality, followed by A and then B. Refrigerated eggs maintained their AA grade for 15 weeks, while unrefrigerated eggs dropped to B grade within a week.

Moreover, it took less than 24 hours for the physical qualities of the room temperature egg yolks (height, width) to be impacted more than the three refrigerated types were over the course of 15 weeks.

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Egg cuticles offer limited protection

Eggs are governed by state and federal standards for operations. The eggs you typically buy at the grocery store are washed to ensure quality standards and to reduce the likelihood of spoilage or food-borne illness, Jones says. The process typically involves a warm-water spray wash with a food-safe detergent solution and brushes, followed by a warm sanitizing rinse. Then the eggs are blown dry before being packaged. (Farm eggs from smaller producers may not receive this same treatment, depending on state laws.)

Washing does not happen in some parts of the world - and numerous commenters on our chat argued that this leaves the cuticle on the surface of the shell intact so that the eggs can be stored at room temperature.

But Jones offers this caution: “The cuticle is not for you.” The cuticle is a water-based, higher-protein coating that’s deposited on the egg as it’s being laid. Its purpose is to protect the embryo inside the egg - not protect you against food-borne illness. The cuticle begins to degrade and slough off almost as soon as the egg is laid, to allow for air to reach the embryo in the event it will hatch into a chicken (if the eggs have been fertilized).

Another note about washing: The government does not recommend consumers wash store-bought eggs themselves, as this can introduce bacteria into the eggs. Homegrown eggs can be wiped clean of debris, according to the Colorado State University Extension. If they need to be washed, the water must be between 110 and 120 degrees, and the eggs should never be left to soak.

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Understand the risks

Where you store your eggs is ultimately up to you, and you have to decide how much of a risk you are willing to take and why, Jones says, emphasizing that the government advice is based on “scientific rationale.” Children, elderly people and immune-compromised individuals are more susceptible to complications from food-borne illnesses such as salmonella, but they can lay anyone low.

In the end, there is very little cost - or risk - associated with storing eggs in the refrigerator. I find the benefits of longer-lasting eggs, especially with fluctuating prices, and peace of mind are well worth the fridge real estate.

Because different refrigeration and storage rules may apply to where smaller producers sell eggs, such as directly from their farm or at an organized market, Johnston recommends familiarizing yourself with your state’s rules and inquiring with the producer about their practices.