If you have ever watched a chick hatch, you may have noticed a tiny white or pale point near the tip of its upper beak.
It can look like a little bump, a piece of dried shell, or even a deformity.
It is actually one of the chick’s most important temporary tools. That little structure is called the egg tooth.
But the egg tooth does not work alone. Behind the chick’s head is another temporary hatching tool that most backyard keepers never see.
It is an enlarged neck muscle called the complexus muscle, often called the hatching muscle.
Together, the egg tooth, hatching muscle, head movements, and the chick’s body rotation help it break through the membranes and shell during the final hours of incubation.
That also clears up a common misunderstanding. A mother hen does not normally need to crack every egg open from the outside.
A healthy chick is built to do most of the work itself. If you want the full incubation timeline first, see our Incubating and Hatching Chicken Eggs guide.
What Is the Egg Tooth on a Baby Chick?
The egg tooth is a temporary hard structure near the top of a chick’s upper beak.
Despite the name, it is not a real tooth.
Birds do not develop a tooth made from enamel and dentin for hatching. A 2025 chicken study described the egg tooth as a specialized epithelial structure with a hardened cornified portion called the caruncle.
The researchers found proteins associated with keratinized and cornified tissues. That makes the egg tooth much closer to a temporary hardened beak structure than a true tooth.
So when you see that little white point on a newly hatched chick, you are not looking at an abnormal tooth growing from the beak.
You are looking at a temporary hatching tool.
Is the White Bump on the Chick’s Beak a Deformity?
Usually, no.
If the white bump is sitting where you would expect the egg tooth to be on a newly hatched chick, it is normally part of the hatching process.
Mississippi State Extension describes the egg tooth as a sharp, horny structure on the upper beak. After hatch, the horny cap dries and falls away within days.
That means you may notice it clearly on hatch day and barely see it a few days later.
You do not need to pull it off. It is supposed to be temporary.
Why Does a Chick Need an Egg Tooth?
The shell may look thin when you crack a breakfast egg, but from the chick’s side it is a serious barrier.
The embryo has spent roughly three weeks enclosed by the shell and shell membranes.
Near the end of incubation, the chick has to break through the inner membrane, reach the air cell, crack the shell, enlarge that opening, and finally push its body free.
The egg tooth gives the chick a hard contact point on the beak for that job.
Mississippi State Extension explains that the sharp structure on the upper beak and the muscle at the back of the neck work together to help cut the shell.
There is another helpful change happening at the same time. The eggshell itself is not exactly the same on hatch day as it was when the hen laid it.
During incubation, calcium is mobilized from parts of the shell for the developing chick’s skeleton. Research on eggshell structure shows that the shell becomes progressively altered and weakened toward hatch.
Hatching is therefore more complicated than a tiny spike simply punching through an unchanged shell.
The Egg Tooth Is Only Half of the Hatching Story
The egg tooth gets most of the attention because you can see it.
The more surprising part is hidden behind the chick’s head. This is the musculus complexus, or complexus muscle.
It sits in the upper neck region. Around the hatch, it becomes so enlarged and specialized that poultry researchers commonly call it the hatching muscle or pipping muscle.
The muscle helps support and move the head while the egg tooth is driven against the membrane and shell.
Recent chicken research describes the complexus as an important part of the piercing movement used during hatch. Contraction of this muscle elevates the beak and helps hold the head in position during pipping.
That is why thinking of the egg tooth as a tiny hammer by itself is misleading.
The egg tooth is the hard-working tip. The hatching muscle provides much of the controlled movement behind it.
Is the Complexus Muscle Really Filled With Fluid?
Near hatch, it becomes unusually swollen.
That part of the description is real.
From about embryonic day 17 until hatch, the hatching muscle undergoes rapid enlargement associated with what researchers describe as lymph-like fluid infiltration.
The muscle is also changing internally as it prepares for one of the hardest jobs of the chick’s early life.
You can think of that swelling as part of a temporary power system prepared for the hatch.
But it is better not to describe the muscle as a literal hydraulic piston. The fluid contributes to the swelling while muscle contraction provides the movement that raises and stabilizes the chick’s head and beak.
The Hatching Muscle Grows Very Fast Before Hatch
This is one of the most interesting findings from recent chicken research.
In a 2024 BMC Genomics study, the average hatching-muscle weight increased from about 0.18 grams on embryonic day 15 to about 0.87 grams at hatch.
That is almost a fivefold increase.
The muscle then became much smaller after hatch. Researchers recorded a large decrease within the following 24 hours.
The chick builds a disproportionately large neck muscle just when it needs to escape the egg.
Once the hatch is finished, that extreme enlargement is no longer necessary.
The Complexus Muscle Also Needs a Lot of Energy
Breaking out of an egg is hard work.
Researchers studying the complexus muscle found major changes in its energy metabolism as hatch approached.
The muscle stores and uses glycogen. The 2024 study found that glycogen levels fell sharply around hatch, while creatine-related energy systems also appeared to support the muscle during this work.
This helps explain something you may have noticed if you have hatched chicks before.
A chick may work hard, stop moving, rest for quite a while, and then begin again.
Resting during hatch is not automatically a sign that something is wrong.
Internal Pip Comes Before the Hole You See
When you first notice a small hole in the eggshell, the chick has already completed an important step that you could not see.
That step is called the internal pip.
Late in incubation, the chick normally positions its head near the air cell at the large end of the egg.
The beak breaks through the membrane into that air cell. The chick can then begin breathing air with its lungs and may start peeping while it is still completely inside the shell.
This is why you may sometimes hear a chick before you can see any crack.
For the complete sequence from incubation to hatch day, see our hatching chicken eggs guide.
Then Comes the External Pip
The external pip is the first visible crack or hole in the shell.
Now the egg tooth is working directly against the shell.
Penn State Extension describes the egg tooth making the initial shell break at about day 21 under normal chicken incubation.
Do not expect the chick to burst out immediately after that first hole.
The first external pip is only the beginning of the visible part of the hatch. The chick may stop and rest before it continues.
How Does the Chick Zip Around the Egg?
Once the first opening is made, the chick has to enlarge it.
Backyard keepers call this zipping because the shell develops a line of cracks around its circumference.
The complexus muscle continues to help with forceful head movements, but the muscle does not work alone.
The chick rotates its head and body inside the shell. As it moves, it keeps making cracks around the shell until the top section becomes loose enough to push away.
Mississippi State Extension also describes the chick resting, changing position, continuing to cut the shell, and finally kicking free of the lower part.
So zipping is not the egg tooth sawing around the shell like a tiny can opener.
The egg tooth gives the chick a hard contact point. The complexus muscle helps drive and stabilize the head. The body rotates, and the legs eventually help push the shell apart.
Does the Mother Hen Break the Egg for the Chick?
Normally, the chick has the anatomy needed to hatch by itself.
A broody hen provides the right incubation environment, turns eggs during development, communicates with chicks, and keeps the newly hatched brood warm.
But the actual pipping and shell-breaking work is performed by the chick.
Penn State Extension notes that healthy chicks are able to hatch by themselves and generally advises against routinely helping chicks out of the shell.
That does not mean a hen can never disturb or move a shell during a natural hatch.
It means the hen is not normally cracking each egg open so the chick can climb out.
Why a Pipped Chick May Stop for a While
This is where knowing the biology becomes useful for backyard keepers.
A chick does not usually make one continuous effort from internal pip to standing outside the shell.
There are pauses.
The chick has to breathe, rest, reposition its head and body, and keep supplying energy to one of the most active temporary muscles in its body.
Penn State’s educational material explains that the visible hatching process can take hours.
A pause after pipping is therefore not, by itself, proof that the chick needs help.
If you are using an incubator, humidity, temperature, and ventilation still matter during this stage. Repeatedly opening the incubator or helping too early can create new problems.
What Happens to the Egg Tooth After Hatching?
Once the chick is outside the shell, the egg tooth has finished its main job.
It does not become a permanent part of the adult beak.
Mississippi State Extension says the horny cap falls away within days after hatch.
So if you see the white point on a day-old chick, do not try to remove it.
Let it disappear naturally.
What Happens to the Complexus Muscle?
The hatching muscle also changes quickly after its job is finished.
The 2024 energy-metabolism study found that complexus muscle weight dropped sharply after hatch as the temporary fluid-rich hatching condition disappeared.
But the muscle does not simply vanish.
It transitions into its normal post-hatch role. Research describes the complexus after hatch as helping the chick lift its head during feeding.
A muscle that was highly specialized for escaping the egg becomes part of ordinary movement after the chick is out.
The Eggshell Is Part of the Hatching System Too
It is easy to focus only on the chick.
But the egg itself has been changing throughout incubation.
The developing embryo draws calcium from the inner shell to build its skeleton.
Studies of incubated chicken eggs show progressive changes in shell mineral structure, thickness, hardness, and internal organization.
These changes make calcium available to the embryo and also help make the shell easier to break at the end of development.
So successful hatching depends on several things coming together at the right time.
The chick reaches the correct position. The air cell is available. The lungs begin working. The complexus muscle is fully developed. The egg tooth is hardened. The chick has enough energy. And the shell has undergone its normal incubation changes.
You can follow the earlier stages in our Chicken Life Cycle guide.
Why the Complexus Muscle Matters for Hatchability
The importance of the complexus is not just theoretical.
Researchers studying Naked Neck chickens have looked at whether differences in development of the complexus muscle could contribute to reduced hatchability in some genetic lines.
A 2024 transcriptomic study found changes in genes and pathways related to muscle development and proposed that incomplete development of the complexus could contribute to late embryonic mortality and trouble during hatch.
That does not mean every chick that fails to hatch has a weak complexus muscle.
Incubation temperature, humidity, egg storage, breeder age, embryo position, genetics, ventilation, and other factors can all affect hatch results.
If you are selecting and incubating fertile eggs at home, our How to Breed Chickens guide covers breeder selection, fertility, and hatching eggs.
Can You See the Egg Tooth While Candling?
Usually, not in a useful way.
Candling is much better for checking embryo development, blood vessels, the air cell, movement, and whether an egg appears to be progressing normally.
Near hatch, the egg becomes very dark because the chick fills most of the interior.
The tiny egg tooth itself is not something you should expect to identify clearly through the shell with a normal backyard candler.
You can learn what you can realistically see at different stages in our egg candling guide.
Frequently Asked Questions
Is an egg tooth a real tooth?
No. In chickens, the egg tooth is a temporary cornified epithelial structure on the upper beak. It is made from specialized hardened tissue rather than enamel and dentin like a true tooth.
How long does a chick keep its egg tooth?
Usually only a short time after hatch. Extension sources describe the horny cap drying and falling away within days, so you should not try to remove it yourself.
What is the complexus muscle in a chick?
The complexus is an upper-neck muscle that becomes greatly enlarged before hatch. It helps elevate and stabilize the chick’s head so the egg tooth can be driven against the membranes and shell.
Is the complexus muscle filled with fluid?
It becomes heavily infiltrated with lymph-like fluid before hatch, which contributes to its temporary swelling. The actual hatching movement still comes from active muscle contraction, so it is not a literal hydraulic piston.
Does the mother hen break the shell for the chick?
Healthy chicks normally perform the pipping and shell-breaking work themselves. The hen provides incubation and maternal care, but the chick has its own egg tooth and hatching muscle for getting out of the egg.
Why does a chick stop after making the first hole?
Hatching takes a lot of energy. The chick may pause while breathing, resting, and repositioning before continuing. A pause after pipping does not automatically mean the chick needs assistance.
Does the complexus muscle disappear after hatch?
No. Its unusual hatching enlargement quickly decreases, but the complexus remains as a normal muscle and later helps with ordinary head and neck movement.
Final Thoughts
That tiny white point on a chick’s beak is easy to overlook.
But it is part of a very specialized hatching system.
The egg tooth gives the chick a hard point for breaking membranes and shell. Behind it, the complexus muscle becomes temporarily enlarged and highly active so the chick can lift and drive its head during pipping.
Then the chick rotates inside the egg, continues cracking around the shell, pushes the shell apart, and finally gets free.
Within days, the egg tooth is gone. The oversized hatching muscle rapidly shrinks and changes function.
So neither structure is a defect. They are temporary tools built for one of the hardest jobs a chick will ever do: getting out of the egg.
Sources and Further Reading
- Journal of Developmental Biology (2025) — The Epithelial Egg Tooth of the Chicken Shares Protein Markers with the Embryonic Subperiderm and Feathers
- BMC Genomics (2024) — Gene Ontology Defines Pre-Post-Hatch Energy Dynamics in the Complexus Muscle of Broiler Chickens
- BMC Genomics (2024) — Transcriptional Profiling of the M. Complexus in Naked Neck Chickens
- Penn State Extension / Pennsylvania 4-H — Hatching and Chicken Embryo Development
- Mississippi State University Extension — Stages in Chick Embryo Development
- PubMed — Research on Eggshell Structural Changes During Incubation
