In the United States, eggs must be washed and sanitized before sale, which removes the cuticle (bloom). This is why American eggs require refrigeration — and European eggs don't.
The same question appears repeatedly when Americans travel to Europe or Europeans visit the United States: why are eggs sold at room temperature in European supermarkets while American regulations require refrigeration? The answer is not a difference in the eggs themselves. It is a difference in how the eggs are processed before sale and what that processing does to the egg's natural defenses against bacterial contamination. Both approaches are internally consistent and reasonably effective. They are simply incompatible with each other.
## The Cuticle and Its Protective Function
A freshly laid egg is coated with the cuticle, also called the bloom. This is a thin protein layer applied to the outer shell surface in the final minutes of the egg's passage through the hen's oviduct. The cuticle serves two overlapping functions: it physically blocks many of the shell's thousands of pores, slowing moisture loss and gas exchange, and it provides a chemical and physical barrier against bacterial entry. The cuticle contains antimicrobial compounds and creates a slightly hydrophobic surface that resists water-borne bacterial penetration.
Intact cuticles are the European approach to egg safety. European Union regulations prohibit washing eggs before sale precisely because washing destroys the cuticle. Eggs with intact cuticles can be stored at room temperature safely for several weeks. Once the cuticle is intact and dry, the main risk (Salmonella contamination) is managed by keeping the shell surface dry and not washing it.
## Why the United States Washes Eggs
The United States Department of Agriculture requires eggs to be washed and sanitized at processing facilities. This requirement originated from concerns about Salmonella enteritidis contamination on shell surfaces from contaminated litter and feces in high-density egg production environments. Washing removes surface contamination effectively. But it also removes the cuticle.
Once the cuticle is gone, the egg's primary passive defense against bacterial entry is eliminated. The pores are open. Bacteria on the now-moist shell surface can penetrate through the pores more readily, particularly if condensation forms on a shell that has been refrigerated and then brought to room temperature. Refrigeration addresses this vulnerability directly: at temperatures below 4 degrees Celsius (40 degrees Fahrenheit), bacterial growth (including Salmonella) is dramatically slowed. Cold also reduces condensation on shells kept consistently cold.
## The Condensation Problem
The incompatibility between the two systems is most apparent in practice. If you take a properly refrigerated, washed American egg and leave it at room temperature, condensation may form on the shell as it warms in a humid environment. That moisture, on a cuticle-free shell, creates conditions for bacterial penetration. This is why the USDA recommends keeping washed eggs refrigerated from processing to consumption, and why European eggs should not be refrigerated (refrigerating and then taking out an unwashed egg repeatedly creates condensation on the shell, which can drive water and surface bacteria inward).
Neither system is inherently safer than the other when followed correctly. Both rely on managing Salmonella risk at a different point in the supply chain. The EU also relies heavily on vaccinating laying flocks against Salmonella enteritidis, which reduces the baseline prevalence of contamination significantly. The United States relies more on post-laying sanitation and cold chain management.
For consumers: follow the convention of the country where the eggs were produced. Refrigerate American eggs continuously. Room-temperature storage of cuticle-intact eggs (rare in the US, common in Europe) should be in a cool, dry place out of direct light.