Most eggs are clean when they are laid, but they
can become contaminated with manure or other
foreign material. In the United States, an egg with
manure or adhering material on the shell cannot be
marketed. It is classified as dirty and cannot be used
for human consumption. Eggs with stained shells are
unattractive in appearance and cause eggs to be
downgraded to B quality or dirty depending on the
severity of the stain.