What is a Chicken Egg?

Tricia Christensen
Tricia Christensen

An egg is a vessel that contains an ovum — the reproductive cell produced by a female that would nurture and sustain an embryo. A chicken egg is the egg laid by a chicken. In general, eggs are composed of several parts: they have a hard outer shell, which would help protect a growing bird embryo (if the egg is fertilized); and inside the shell is the ovum. In a fertilized egg, a chick grows inside the egg for about 21 days before it is strong enough to break out of the shell and become a “fully-fledged” chicken.

Chickens actually lay eggs to reproduce, as a fertilized egg will bear a chick.
Chickens actually lay eggs to reproduce, as a fertilized egg will bear a chick.

In most mammals, ova that are unfertilized are periodically shed with the special lining of the uterus that would help nurture a growing fetus. Fertilized ova stay in place and become part of the building blocks that grows into an infant mammal. Chicken eggs are different in this respect, since hens lay both fertilized and unfertilized eggs, and most of the development of the chicken embryo in fertilized eggs occurs outside of the hen’s body. Special care of a fertilized egg is required for a chick to grow and hatch.

The interior of a chicken egg is what people usually eat, after discarding the shell.
The interior of a chicken egg is what people usually eat, after discarding the shell.

There are two main components of the ova in chicken eggs: the albumen or “white” of the egg and the vitellus or yolk. Most people will note some thick milky white membranous structures in the egg too. When not providing nutrition for growing chickens, these eggs are a source of nutrition for people and for animals that eat them. In fact, of all eggs consumed by people, those from chickens are most common, and recipes calling for eggs tend to mean ones from hens, unless they specify otherwise. Though there are specialty markets that sell emu, ostrich, quail, and duck eggs, these remain a tiny percentage of most eggs purchased by humans.

Brown and white chicken eggs.
Brown and white chicken eggs.

While the chicken was once hailed as perhaps a perfect food for humans, there are some concerns about consuming too many eggs. Though a single egg isn’t tremendously high in calories, the yolks do contain high levels of cholesterol. Some people avoid this issue by simply eating egg whites instead, which are high in protein, although not everyone enjoys eating the whites alone. There’s also some argument that sources of cholesterol in egg yolks may actually help lower overall bad cholesterol count, though this issue is debated.

Eggs are considered healthy by many, since they are high in protein.
Eggs are considered healthy by many, since they are high in protein.

Most people stick to eating the interior of the egg and either discard or compost the shells. Actually, eggshells are edible, and some people blend them into shakes. Eggshells may also constitute part of chicken feed since they have nutritive value. Different breeds of chickens lay eggs of different colors, but this has no direct impact on the taste or nutritional value of the egg itself.

A chick and an egg.
A chick and an egg.

One thing that may prove confusing for people is the different grades of chicken eggs and their different sizes. Eggs come in peewee, small, medium, large, extra-large, and jumbo in the US, although "large" is the most common size used. Moreover, some eggs are labeled organic and others may be sold as created by free-range chickens. The country in which the eggs are produced usually regulates the definitions of each of these terms and grades. Typically, free range and organic eggs will cost most, but the price is usually higher for larger eggs too. Some people purchase fertilized eggs because they’re lower in cholesterol.

Laying eggs is an evolutionary holdover from the dinosaur ancestors of modern birds.
Laying eggs is an evolutionary holdover from the dinosaur ancestors of modern birds.
A large egg can contain about 225 mg of cholesterol, or most of the average person's daily allowance.
A large egg can contain about 225 mg of cholesterol, or most of the average person's daily allowance.
Tricia Christensen
Tricia Christensen

Tricia has a Literature degree from Sonoma State University and has been a frequent wiseGEEK contributor for many years. She is especially passionate about reading and writing, although her other interests include medicine, art, film, history, politics, ethics, and religion. Tricia lives in Northern California and is currently working on her first novel.

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Discussion Comments


My dad grew up on a farm where they had a lot of chickens. They would gather the eggs, and whatever wasn't needed for their family, they would sell.

This is something that many farm families still do today. I have always been kind of afraid of chickens and don't know how comfortable I would be reaching in and grabbing the eggs.

This article also reminds me of the age-old question of which came first, the chicken or the egg?

It doesn't seem like you hear as much any more about how chicken eggs are so high in cholesterol. Is it the yolk that gives them the high cholesterol content? I always thought eggs were full of good nutrition, and a cheap meal when I was a poor college student.

I feel very fortunate to have a neighbor who sells farm fresh chicken eggs. I don't think she can consider them organic or even free range, but I can see how they are fed and taken care of, and feel safe buying eggs from her.

I don't usually have any problem getting as many eggs from her as I need. If there is a big salmonella scare though, people are afraid to buy eggs in the store, and sometimes she runs out of them.


I grew up on the farm and was used to eating brown eggs with bright yellow yolks. Whenever we had overnight guests, they always commented on how yellow our eggs were.

I always thought that was a funny comment because that is all I had ever known. Not until I moved to the city and began buying eggs in the store did I realize what they meant. I also realized that the shells on our chicken eggs at home were much thicker and harder to crack.

Now I go out of my way to buy brown eggs that are either organic or free range. Some stores carry them, and I can also find some at farmers markets. Sure, I pay more for a dozen of them, but overall, eggs are still pretty cheap when you consider how much nutrition and protein you are receiving from them.


@kylee07drg – The easiest way is to use a funnel. My friend taught me this trick a few months ago, and it has opened up a whole new world of recipes to me, because I had the same problem as you.

The yolk is too large to go through the narrow hole in the funnel. However, the egg white will slip right on through. Just be sure you have a mixing bowl beneath the funnel to catch the egg white.


So many recipes, especially desserts, call for egg whites. I have always had trouble separating them from the yolks, so I just avoid these recipes.

Can anyone tell me what the best way to separate an egg white from a yolk is? I can't do it using just the shells like some people can.


Some people think it's a little weird to cook chicken and eggs together, but I do it all the time. I dip raw chicken in eggs and milk before rolling it in seasoned flour and frying it.

My husband also makes an excellent chicken teriyaki meal that uses both chunks of chicken and bits of scrambled egg. It's so delicious, and you might not think this would be true, but chicken and eggs taste great together!


My mother actually got to witness hatching chicken eggs when she was young. Her family raised their own chickens, and they ate some of the eggs, but the ones they didn't eat got to develop into more chickens.

It seems a little unsanitary to eat something that a chicken has been sitting on top of for awhile. I try not to think about this while eating scrambled eggs!


@liveoak- I know what you mean about not having a clue about eating the shells. I could even grind up the shells into a powder and put them in soups or other foods. I will also think about how I am going to use the shells the next time I buy eggs.


I had no idea that you can eat the shell of an egg. I always thought that they should just be thrown out. To think I have been throwing out something with nutritional value all these years is kind of sad. The next time I see chicken eggs for sale I will definitely try eating the shell in a shake.

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