Eggshell Spots Do Not Always Mean an Egg Has Spoiled, Expert Says

Dragon Media Newsroom

Spots on an eggshell do not by themselves prove that an egg has spoiled. Zheng Jiangxia, a professor at the College of Animal Science and Technology at China Agricultural University, says eggshell spots vary in appearance and cause. Some spotted eggs are safe to eat, while eggs with mold spots or cracked shells should be avoided.

Brown or black spots, which may be slightly raised, can form when pigment is deposited unevenly on the shell. They may be related to a hen’s condition while laying—for example, a vitamin A deficiency or excessive calcium intake. Similar spots can also appear in first-time layers because their reproductive tract is narrow. These spots do not make the eggs unsafe to eat.

Dark, water-mark-like spots beneath the shell can develop when the shell membrane is weak and moisture from inside the egg passes through and collects on the shell. Such spots do not significantly affect egg quality and are not necessarily linked to contamination by pathogens, the expert said. They are more likely to appear in hot, humid weather, when laying hens may experience heat stress. The spots may become visible about three days after the egg is laid and can gradually fade during storage.

However, mold spots can develop when eggs are stored for a long time in a hot, humid and poorly ventilated place. They appear opaque when held up to a light, and mold may be visible on the shell after the egg is cracked. Such eggs should not be eaten. The university’s guidance also advises against eating eggs with fine cracks in the shell, as the damaged barrier can allow bacteria to enter.