An egg is not sealed shut. Its shell carries several thousand microscopic pores, and how long the egg inside stays good is almost entirely a story about what plugs them. A refrigerated egg in the U.S. is good for three to five weeks past the day you bring it home, while the same egg sold in much of Europe is expected to move off the shelf within days — same egg, same shell, wildly different clock.
Why refrigeration means something different in the US
Every egg leaves the hen coated in a thin protein film called the cuticle, or bloom, laid down as the last step before laying. It seals the pores in the shell. Sealed pores are what keep bacteria out and moisture in, and an intact cuticle is a genuinely good barrier on its own.
U.S. regulations require commercial eggs to be washed and sanitized before they reach a store, and washing strips the cuticle along with the dirt. Once that coating is gone, the pores are open, so USDA guidance requires the eggs to stay below 40°F (4°C) from then on. Cold slows bacterial growth enough to compensate for the barrier that scrubbing removed.
Most of Europe skips the wash. Cuticle intact, the eggs are sold and kept at room temperature, and refrigerating one after purchase can do more harm than good: pull a cold egg back out into a warm kitchen and moisture condenses on the shell, which is exactly the kind of film that lets bacteria travel through an intact cuticle's few weak points. Two systems, two correct answers, one missing coating explaining the entire difference.
Why a fresh egg sinks and an old one floats
The cuticle slows moisture and carbon dioxide loss through those pores. It does not stop it. Every day an egg sits, a little of both escape, and the air pocket at the blunt end — present in every egg from the moment it cools after laying — gets a bit bigger to fill the space that leaves.
That is the entire mechanism behind the float test. Submerge an egg in water: a fresh one has a small air cell and lies flat on the bottom. Three or four weeks in, the air cell has grown enough that the egg tilts upright. Past that, it floats outright, because it now displaces less water than the air trapped inside it. None of this means the egg is bad. It means it is older, and an older egg has a thinner white and a flatter yolk — good enough for scrambling or baking, not what you want for a poached egg with a tight, high-standing white.
That decline is not spoilage. It is water and gas leaving through pores that were always going to let them out eventually.
The smell test, and the one real risk
Actual spoilage is bacterial, not chemical, and it announces itself. A rotten egg smells sulfurous the moment you crack it — the compound is hydrogen sulfide, produced by bacteria breaking down the proteins inside — and there is no ambiguity about it once you catch a whiff. If an egg smells fine, it is fine to eat, regardless of how long it floats.
Salmonella is the genuine risk here, and it gets in through the same open pores that force refrigeration in the first place: a cracked shell, or a washed shell left too long above 40°F (4°C), gives bacteria already on the surface a path inside. That is a real hazard, not a hypothetical one, which is exactly why the temperature rule exists rather than being optional advice.
How long eggs last, by storage method
Everything below assumes the egg started fresh and stayed cold. A warm kitchen counter shortens all of these.
| Form | How long it keeps |
|---|---|
| Raw, in the shell, refrigerated | 3–5 weeks |
| Raw, out of the shell, refrigerated | 2–4 days |
| Hard-boiled, refrigerated | About 1 week |
| Raw, whisked, frozen | About 1 year |