Why Does a Green Ring Appear Around Hard-Boiled Eggs?

Hard-boiled eggs are one of the most popular and convenient protein sources in the world. They’re used in breakfast meals, salads, sandwiches, and even appetizers. Yet, despite being easy to prepare, a common issue often surprises many home cooks: a greenish-gray ring around the yolk. This unexpected discoloration can raise questions—Is the egg spoiled? Is it still safe to eat? Did something go wrong during cooking?

In this article, we’ll explain why that green ring forms, how to prevent it, whether it’s safe to eat, and how it might even affect the nutritional quality of your eggs.

The green ring that sometimes appears around the yolk of a hard-boiled egg is the result of a chemical reaction. It occurs when sulfur from the egg white reacts with iron from the yolk. This typically happens during overcooking or when the eggs are exposed to high heat for too long.

Specifically, when eggs are boiled for too long or at too high a temperature, sulfur compounds in the white begin to break down. These compounds then migrate toward the yolk, where they interact with iron to form ferrous sulfide—a substance with a green or grayish color.