American eggs carry salmonella risk primarily because of how the bacteria infects hens internally, combined with a regulatory approach that prioritizes washing and refrigeration over vaccinating flocks. The US strategy removes bacteria from the outside of the shell but also strips away the egg’s natural protective coating, creating a system where refrigeration becomes essential and any break in the cold chain can allow bacteria to multiply.
How Salmonella Gets Inside the Egg
Salmonella doesn’t just sit on the outside of an eggshell. The bacterium, specifically a strain called Salmonella Enteritidis, can colonize a hen’s ovaries and reproductive tract. When this happens, the egg can become contaminated internally while it’s still forming inside the bird, before the shell even exists. Researchers have confirmed through tissue staining that the bacteria colonize oviduct tissues associated with developing eggs, meaning the yolk or white can carry salmonella from the moment of formation.
There are two routes of contamination. Vertical transmission happens when bacteria pass from infected ovarian or oviduct tissue directly into the egg contents during formation. Horizontal transmission occurs when bacteria from the environment, feces, contaminated feed, or the hen’s cloaca land on the shell surface and potentially penetrate through the pores. Studies have found that horizontal contamination of eggshells is far more common (around 58% of eggs from infected flocks in one study), while internal contamination through vertical transmission is rarer, closer to 5%. But that internal contamination is the more dangerous kind, because no amount of shell cleaning can address it.
The Washing Tradeoff
In the US, commercial eggs go through a mechanical washing process almost immediately after being laid. The shells are scrubbed with hot water (at least 90°F, and at least 20°F warmer than the eggs themselves), using approved cleaning compounds. The process is designed to be fast and continuous, with eggs never allowed to sit or soak in water. This removes visible dirt, fecal matter, and bacteria from the surface effectively.
But washing also removes something important: the cuticle. Every egg comes with a thin, barely visible protein coating called the bloom or cuticle that naturally seals the shell’s microscopic pores. This layer acts as a barrier against bacteria. Once it’s scrubbed off, the shell becomes more porous and vulnerable to contamination from the environment. To compensate, US producers spray the washed eggs with a thin layer of oil and then refrigerate them. Federal law requires all shell eggs packed for consumers to be stored and transported at no more than 45°F (7.2°C). Small producers with 3,000 or fewer hens are exempt from this requirement.
This is the core of the American approach: clean the shell aggressively, then protect the now-vulnerable egg with refrigeration for the rest of its journey to your kitchen.
Why Most Other Countries Don’t Wash Eggs
Many countries, particularly in Europe, take the opposite approach. Rather than washing eggs and relying on cold storage, they leave the cuticle intact and focus on preventing infection at the source. In the UK and several EU nations, egg-laying hens are vaccinated against Salmonella Enteritidis. This dramatically reduces the chance that a hen’s reproductive tract carries the bacteria in the first place.
Vaccination works. Research on commercial flocks showed that vaccinated hens had salmonella in their reproductive tracts at a rate of about 14%, compared to nearly 52% in unvaccinated hens. Gut colonization dropped from 64% to 38%. These reductions carried through the entire production chain, with lower contamination rates in chicks, farm environments, and birds entering processing plants. The US does not require salmonella vaccination for laying hens. Some producers vaccinate voluntarily, but it’s not a universal practice.
As one poultry veterinarian and adviser to the International Egg Commission put it, the two systems are “different approaches to basically achieve the same result.” Neither side of the Atlantic has a massive food safety crisis. But the American system depends on an unbroken cold chain, while the European system depends on healthier flocks.
What Changed With the 2010 Egg Safety Rule
Before 2010, US egg producers had relatively few federal requirements around salmonella prevention in the henhouse itself. The FDA’s Egg Safety Final Rule changed that, requiring virtually all producers with 3,000 or more laying hens to adopt preventive measures during production. These include environmental testing for Salmonella Enteritidis in poultry houses, along with mandatory refrigeration during storage and transportation. Eggs processed with a kill step like pasteurization are exempt, since the treatment handles the bacteria directly.
The rule was a significant step, but it still relies on testing and refrigeration rather than eliminating the bacteria from flocks through vaccination. The result is a system where contaminated eggs can still enter the supply chain, and the safety net is proper handling from farm to table.
Why Refrigeration Matters So Much
Once an egg has been washed and its cuticle removed, refrigeration isn’t optional. If a contaminated egg warms up, any salmonella present (whether on the shell surface or inside) can begin multiplying. A single bacterium on a warm egg can become millions within hours. Keeping eggs at or below 45°F slows bacterial growth to a near standstill.
This is also why you can’t buy American eggs, leave them on the counter for a week as you might in France, and expect them to be safe. The washing process committed those eggs to the cold chain. Breaking it doesn’t just reduce freshness; it creates conditions for bacterial growth that the intact cuticle would have naturally prevented.
Cooking Temperatures That Kill Salmonella
Regardless of how eggs are produced or stored, cooking is the final safeguard. Salmonella is reliably destroyed when food reaches 150°F and stays there for at least 12 minutes, or 140°F held for about 45 minutes when contamination levels are low. In practical terms, this means fully cooked eggs (scrambled, hard-boiled, or baked into dishes) pose virtually no salmonella risk. The danger zone is undercooked preparations: runny yolks, homemade mayonnaise, raw cookie dough, or eggs Benedict with a soft poach.
If you prefer your eggs with a liquid yolk, pasteurized eggs are available in most US grocery stores. These have been heat-treated just enough to kill bacteria without fully cooking the egg, making them safe for preparations where the egg won’t reach high temperatures.
The Bottom Line on American Eggs
American eggs have a salmonella concern not because US chickens are inherently dirtier, but because the country chose a regulatory path built around washing, oiling, and refrigerating eggs rather than vaccinating hens. That choice strips the egg’s natural defense, creates dependence on cold storage, and does nothing to address the bacteria living inside a hen’s reproductive tract. The system works when every link in the chain performs correctly, but it leaves less margin for error than a vaccination-first approach.