The chance of getting salmonella from any single raw egg is low, but it is not zero. Most large-scale surveys find that somewhere between one in a few hundred and one in a few thousand commercially produced eggs carry the bacterium, and even when a contaminated egg slips through, the dose is usually tiny enough that your immune system can handle it. One quantitative risk assessment estimated the probability of illness from eating an uncooked egg at roughly two in ten million per serving, which sounds reassuring until you consider that billions of eggs are consumed every year and some people eat raw or undercooked eggs regularly.1PubMed Central. Quantitative risk assessment of foodborne Salmonella illness by estimating cooking effect on eggs from retail markets The real story, though, depends on where your egg came from, how it was stored, and what you do with it in the kitchen.
How Often Are Eggs Actually Contaminated?
Prevalence numbers vary wildly depending on the country, the production system, and the stage of the supply chain where testing happens. A study sampling eggs in both conventional battery-cage and alternative cage-free systems in the United States found zero positives out of 240 conventional eggs. Cage-free eggs fared slightly worse, with about one percent of samples carrying Salmonella.2PubMed Central. Prevalence of Salmonella in Eggs from Conventional and Cage-Free Egg Production Systems and the Role of Consumers in Reducing Household Contamination A separate study testing over 200 eggs from retail markets found none positive at all.1PubMed Central. Quantitative risk assessment of foodborne Salmonella illness by estimating cooking effect on eggs from retail markets
Those numbers look encouraging, but they represent a snapshot from regulated systems with refrigeration, washing, and inspection. In China, a meta-analysis across multiple production stages found contamination rates around ten percent at the farm level, dropping to roughly one percent by the time eggs reached the point of sale or consumption.3PubMed. A meta-analysis and systematic review of Salmonella prevalence in table eggs from China and the efficacy of inactivation technologies for Salmonella in table eggs Open-style farms, where birds have more contact with the environment, showed rates pushing toward nineteen percent. The takeaway is that production practices, regulatory standards, and how quickly eggs get refrigerated after laying all shape the contamination rate you’re actually exposed to.
How Salmonella Gets Into an Egg
There are two routes. The first is transovarian transmission, where the hen’s reproductive tract is infected and Salmonella ends up inside the egg before the shell even forms. This is the route that makes raw eggs risky no matter how clean the shell looks. The second is shell penetration: bacteria from feces or the environment land on the shell and, given the right temperature and moisture conditions, migrate inward through the pores.
Egg washing, which is standard practice in the United States and several other countries, targets the second route. Under optimized conditions, washing can reduce Salmonella counts on the shell surface by more than a hundred-thousand-fold. But temperature control during washing turns out to be critical. If the wash or rinse water is too cool, the temperature difference can actually draw bacteria through the shell pores and into the egg’s interior.4ScienceDirect (Journal of Food Protection). An Assessment of the Microbiological Risks Involved with Egg Washing under Commercial Conditions Countries in the European Union generally skip washing and instead rely on vaccination programs and refrigeration-free shelf-stable cuticles, which is one reason you’ll see unrefrigerated eggs on grocery shelves in Europe but not in North America.
The Egg’s Built-In Defenses
An egg is not a helpless vessel waiting for bacteria to move in. Egg white is a surprisingly hostile environment for microbes, and most of its defensive power comes down to starving bacteria of iron. Ovotransferrin, a protein that makes up a significant chunk of egg white, binds iron so tightly that bacteria reliant on it for growth simply cannot multiply.5PubMed Central. The anti-bacterial iron-restriction defence mechanisms of egg white; the potential role of three lipocalin-like proteins in resistance against Salmonella Lysozyme, another egg white protein, directly attacks bacterial cell walls.
These defenses are not static. Research on hens across an extended production cycle found that concentrations of both lysozyme and ovotransferrin actually increase as hens age. Eggs from older hens showed the strongest ability to suppress Salmonella growth, even when challenged with high bacterial loads. The study also noted that eggs which remained uncontaminated had measurably higher concentrations of these antimicrobial proteins, suggesting the defenses do real work in keeping bacteria at bay.6PubMed. Antimicrobial defenses of table eggs: Importance of antibacterial proteins in egg white as a function of hen age in an extended production cycle The catch is that these defenses are strongest in the egg white. Once bacteria reach the nutrient-rich yolk, the picture changes completely.
Why Refrigeration Changes Everything
Temperature is the single biggest controllable factor in whether a contaminated egg becomes dangerous. In experiments where Salmonella was introduced into egg yolk and stored at room temperature (about 25°C or 77°F), bacterial counts skyrocketed within four days, growing by nearly ten thousand fold in the yolk.7PubMed Central. Refrigeration of eggs influences the virulence of Salmonella Typhimurium Even when bacteria were introduced into the egg white rather than the yolk, they migrated to the yolk and multiplied there. The yolk’s rich nutrient content is essentially an all-you-can-eat buffet for Salmonella once the egg white’s iron-restriction defenses are breached.
At refrigerator temperature (5°C or 41°F), the story flips. Bacterial counts stayed flat over the same four-day window. The bacteria survived at refrigerator temperature but could not meaningfully grow.7PubMed Central. Refrigeration of eggs influences the virulence of Salmonella Typhimurium Separate research showed a consistent pattern: for every five-degree Celsius rise in storage temperature, Salmonella multiplication in egg yolks increased substantially. At 10°C, there was only modest growth after 24 hours. At 25°C, the bacteria reached concentrations thousands of times higher.8Journal of Food Protection. Multiplication of Salmonella Enteritidis in Egg Yolks after Inoculation outside, on, and inside Vitelline Membranes and Storage at Different Temperatures
This means that a contaminated egg sitting on your counter for a few hours is a very different risk proposition from a contaminated egg that has been refrigerated continuously. If you plan to eat eggs raw or lightly cooked, keeping them cold until the moment you use them is not just good practice, it is the most important thing you can do.
Raw Versus Cooked and What Counts as “Done”
Cooking is the second line of defense, and it is devastatingly effective. Salmonella dies rapidly at temperatures above about 60°C (140°F). In whole egg, ninety percent of the bacteria are destroyed in roughly 16 seconds at that temperature.9PubMed Central. Heat resistance of Salmonella in various egg products The quantitative risk assessment mentioned earlier found that the probability of illness from a cooked egg was around 350 times lower than from a raw one.1PubMed Central. Quantitative risk assessment of foodborne Salmonella illness by estimating cooking effect on eggs from retail markets
There are wrinkles, though. Egg yolk mixed with sugar or salt is harder to sterilize by heat. Adding ten percent salt to yolk dramatically increases the time needed to kill the same fraction of bacteria, roughly tenfold compared with plain yolk at the same temperature.9PubMed Central. Heat resistance of Salmonella in various egg products This matters for homemade ice cream bases, custards, and salted egg preparations, where sugar or salt may be mixed into raw egg and the mixture never reaches a full cooking temperature.
Soft-boiled eggs and sunny-side-up eggs fall in a gray zone. If the yolk stays runny, the center may not reach 60°C. For a healthy adult, that residual risk is small. For young children, older adults, pregnant women, or anyone with a compromised immune system, the standard advice from food safety agencies to cook eggs until both the white and yolk are firm exists for good reason.
Kitchen Habits That Quietly Raise Your Risk
When people do get sick from eggs, it often has less to do with eating a single raw egg and more to do with how eggs are handled in the kitchen. Pooling eggs, where you crack several into a single bowl for scrambling or baking, is standard practice. But if even one of those eggs carries Salmonella, every egg in the pool is now contaminated. A survey of food-service kitchens in the United Kingdom found that pooled raw shell egg mix was routinely prepared by whisking, and that the act of whisking, especially with an electric whisk, aerosolized tiny droplets. Salmonella could be recovered from work surfaces some distance from the mixing bowl and persisted for up to 24 hours in dried egg residue.10Journal of Food Protection. Pooling Raw Shell Eggs: Salmonella Contamination and High Risk Practices in the United Kingdom Food Service Sector
Cross-contamination from raw egg on hands is another underappreciated route. A study of consumers in Romania and Portugal found consistent positive correlations between how often people ate raw-egg dishes, how infrequently they washed their hands after handling raw eggs, and how many foodborne illness events their households reported.11Food Control. Raw-egg based-foods consumption and food handling practices: A recipe for foodborne diseases among Romanian and Portuguese consumers The correlation worked in both directions: more hand washing after handling raw eggs was linked to fewer illness events. The practical message is straightforward. Wash your hands and any surface that touched raw egg before you move on to the next task.
Pasteurized Eggs and In-Shell Treatment
If you regularly make recipes that call for raw or barely cooked eggs, such as Caesar dressing, homemade mayonnaise, mousse, or meringue, pasteurized eggs largely eliminate the Salmonella question. In-shell pasteurization heats the egg to about 55°C (131°F) and holds it there long enough to destroy bacteria without visibly cooking the egg. Research has demonstrated that this process can achieve a ten-million-fold reduction in Salmonella counts while preserving the egg’s functional and visual quality.12PubMed. Pasteurization of eggs in the shell
The standard thermal pasteurization method, holding at around 57°C for nearly an hour, works but adds cost and can slightly affect egg white proteins. Newer approaches using radio frequency heating can penetrate the shell more evenly, reduce processing time, and maintain quality better than the traditional method. Nonthermal technologies, including ultraviolet light, ozone, and cold plasma, are also being explored for surface decontamination of intact eggs.13PubMed. A review on egg pasteurization and disinfection: Traditional and novel processing technologies Pasteurized shell eggs are available in many grocery stores and are labeled as such. Liquid pasteurized egg products, sold in cartons, are another option for recipes where whole-egg form is not required.
Vaccination and What Happens Before the Egg Reaches You
Much of the progress in reducing Salmonella in eggs has happened on the farm, not in the kitchen. Vaccinating laying hens against Salmonella Enteritidis, the strain most commonly associated with egg contamination, has become standard practice in many countries. A study evaluating vaccination across multiple Salmonella strains found that vaccinated flocks had significantly fewer positive eggshells and roughly half the rate of contaminated egg contents compared to unvaccinated flocks.14PubMed. Estimation of the impact of vaccination on faecal shedding and organ and egg contamination for Salmonella Enteritidis, Salmonella Typhiumurium and monophasic Salmonella Typhimurium Vaccination does not completely prevent egg contamination, but it meaningfully reduces it.
Vaccine schedules matter, too. Research on live Salmonella Enteritidis vaccines found that hens given three doses during the rearing period, rather than just one or two, showed higher protection throughout the entire laying period, with lower excretion, less organ colonization, and fewer contaminated eggs.15Poultry Science. Evaluation of different live Salmonella enteritidis vaccine schedules administered during layer hen rearing to reduce excretion, organ colonization, and egg contamination In trials of an experimental attenuated vaccine, egg contamination rates in vaccinated groups dropped to as low as zero in some weeks, compared with rates above twenty-five percent in unvaccinated controls, especially when booster doses were given orally.16PubMed. Efficacy for a new live attenuated Salmonella Enteritidis vaccine candidate to reduce internal egg contamination
These farm-level interventions are a major reason why Salmonella rates in commercial eggs have dropped in many developed countries over the past few decades. They are also why the distinction between commercially produced eggs and eggs from other sources matters for your risk.
Backyard Flocks and Small-Scale Production
If you keep backyard chickens or buy eggs from a neighbor’s small flock, the risk calculation shifts. Backyard birds are rarely vaccinated against Salmonella, they have contact with wild birds and rodents that can carry the bacterium, and their eggs typically are not washed, refrigerated, or inspected on the same timeline as commercial eggs. Between 1996 and 2012, at least 45 outbreaks of human Salmonella infections in the United States were linked to live poultry from mail-order hatcheries, and backyard flock contact has been a recurring source of human salmonellosis.17PubMed Central. Backyard poultry flocks and salmonellosis: a recurring, yet preventable public health challenge
This does not mean backyard eggs are dangerous by default. Many small-flock keepers maintain clean coops and collect eggs promptly. But it does mean that the very low contamination rates found in studies of commercial eggs should not be assumed to apply to unregulated, unvaccinated flocks. If you get eggs from a backyard source, refrigerating them immediately, using them quickly, and cooking them thoroughly makes more of a difference than it does for store-bought eggs.
Duck Eggs and Other Species
Chicken eggs get most of the attention, but duck eggs are widely consumed in parts of Asia and are used in specialty recipes elsewhere. A study at a traditional market in Indonesia found Salmonella in duck eggs but not in chicken eggs from the same market.18Tropical Health and Medical Research. Salmonella sp Contamination on Chicken Eggs and Duck Eggs at the Antasari Traditional Market, Banjarmasin, Indonesia That is a small sample from one market, so it does not prove duck eggs are universally riskier. But ducks are ground-nesting birds whose eggs come into close contact with soil, water, and feces, so the contamination pathway through the shell is more common. Quail eggs, used raw in some cuisines, carry similar considerations and are less studied.
How Salmonella Enteritidis Became a Global Problem
The particular strain of Salmonella most strongly associated with egg contamination, Salmonella Enteritidis, did not become a worldwide issue by accident. A genomic analysis integrating over 30,000 Salmonella Enteritidis genomes from 98 countries traced the global spread of this strain to the centralized sourcing and international trade of poultry breeding stocks beginning in the early 1980s. As a small number of breeding companies supplied parent stock to commercial egg operations around the world, the bacterium hitched a ride. Between 2015 and 2018, Salmonella Enteritidis-contaminated eggs caused the largest known salmonellosis outbreak in Europe, with over 1,200 reported cases across 16 countries.19Nature Communications. Global spread of Salmonella Enteritidis via centralized sourcing and international trade of poultry breeding stocks
This history explains why vaccination and biosecurity programs at the breeding-stock level, not just at the laying farm, are considered important by regulators. It also puts current contamination rates in perspective: the reason eggs are as safe as they are today reflects decades of targeted intervention at every level of the supply chain, from the grandparent flocks that produce breeding hens down to the wash water temperature at the packing plant. The risk has not been eliminated, but it has been driven to historically low levels in countries with strong food safety infrastructure. Where that infrastructure is weaker or where production is less centralized, the numbers can be meaningfully higher.