The eggs, being referred to in Chinese media and on the internet as "rubber eggs" or "ping pong eggs," are too hard to eat, raising suspicion they are fake, after appearing in "small numbers" in markets nationwide, Xinhua news agency said.
"The investigation is designed to appease consumers' concerns, after some suspected they bought artificial eggs made by unconscientious traders seeking profits," it reported.
However, the eggs' hardness could be a natural occurrence, caused by hens consuming large amounts of food enriched with a compound called gossypol, which binds to protein in egg yolks, Xinhua said.
"While gossypol normally exists in the residue of cotton seeds added to chicken feed as an extra protein source, large doses of the compound will suppress sperm activity as gossypol has been tested to be used in male contraceptive pills," it added.
