Why is the yolk of my hard-boiled egg turning green?

 

If you’ve ever sliced open a hard-boiled egg and found a greenish or gray ring around the yolk, it can look… unsettling. The good news: it’s completely harmless and very common.

What causes the green ring?

That discoloration is the result of a simple chemical reaction.

When eggs are cooked too long or at too high a temperature, sulfur in the egg white reacts with iron in the yolk. This creates a compound called , which forms that green-gray layer around the yolk.

So, it’s not spoilage—it’s just overcooking.

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