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An eggshell may look solid, but it contains 7,000 to 17,000 microscopic pores. These tiny openings allow oxygen to enter and carbon dioxide and moisture to leave, helping a developing chick breathe inside the egg. To protect the egg, the shell is covered by a thin outer coating called the cuticle, which helps block bacteria from entering. Washing eggs can remove this protective layer, which is why egg handling practices differ between countries.
The eggshell is a remarkable natural design that balances protection with the need for gas exchange.
© United States Department of Agriculture