1. Why a Baby's Ear Is Not Just a Tiny Adult Ear
If you look at a baby’s ear, it might seem like just a small version of an adult’s ear. However, different parts of the ear grow at very different times. The part on the outside that collects sound is called the pinna (or auricle). In studies measuring the pinna, most dimensions at birth are 52 to 76 percent of adult sizes. The small bump in front of the ear canal opening, called the tragus, was less than half the length and height of an adult’s [3].
In contrast, the cochlea, which is deep inside the ear and senses sound, grows early. A paper studying fetal inner ears reports that the cochlea reaches almost adult size by about 23 weeks of pregnancy [1]. However, this refers only to physical size. It does not mean a baby hears exactly like an adult.
The outer ear grows after birth, while the inner ear is nearly complete before birth. This difference in timing is the key point of this article. So, how long does the outer part keep growing?
2. How the Outer Ear (Pinna) Keeps Growing Until the Teenage Years
The pinna grows very quickly during the first 3 to 6 months after birth, then continues slowly toward adult size [3]. When does it reach adult dimensions? A review of studies reports that ear width reaches adult values between ages 5 and 11. Ear length reaches adult values between ages 12 and 16 [4]. Another report suggests ear height matures at age 13 for boys and age 12 for girls.
These numbers come from past studies and show a range of ages. Still, it is clear that the outer ear continues to grow through elementary school and into middle school. It is not just the outer flap that grows. The ear canal itself also develops. If the ear canal changes, what happens to the sounds entering the ear?
3. Why a Short Ear Canal Rings at High Pitches
The ear canal is a tube that lets sound pass through to the eardrum. Tubes have pitches where they ring easily. The shorter the tube, the higher the pitch it rings at. This is the same relationship as with flutes: a short flute makes high sounds, and a long flute makes low sounds.
The ear canal of an infant is described as being about half the length and width of an adult’s [5]. Because of this, the pitch at which it rings should be different from an adult’s. In research on resonance frequency and age, the peak ringing pitch was higher for younger children. For 4-year-olds, the average was about 3089 Hz (range: 2298 to 3763 Hz). This pitch drops with age and reaches adult levels around age 7 [5]. Note that this data is for toddlers; newborns and infants are measured differently, so their values differ.
For adults, the whole ear, including the pinna and head, resonates to boost sounds near 2700 Hz by about 17 dB [6]. This means a band of sound close to the pitch of human speech gets stronger when it enters the ear. This value is for the whole ear, not just the canal.
The growth of the outer ear moves the pitch where sounds get boosted. So, what about the inside of the ear?
4. The Inner Ear (Cochlea): Size Is Fixed Before Birth, But Function Develops
The size of the cochlea is mostly set before birth. Even so, materials from an acoustics conference state that even if the cochlea’s structure is thought to be complete at birth, indicators of ear function, such as otoacoustic emissions, show immaturity after birth [2].
The middle ear, behind the eardrum, also shows signs of ongoing development. A study measuring infants aged 1 to 24 months and adults found that infants’ middle ear impedance differs from adults’. This means energy is transmitted differently in babies [7].
Do not read this as "babies cannot hear." The study only shows that sound transmission differs between infants and adults. The outer ear, ear canal, middle ear, and cochlea each develop at different times. Does ear growth stop when we become adults?
Note: The sources used here do not tell us if children’s hearing is better or worse than adults’.
5. Do Ears Get Longer Even in Adulthood? A Study of 206 Patients
In 1995, a British doctor named Heathcote measured the ear length (from the lobe attachment to the top) of 206 patients aged 30 and older. The average was 67.5 mm. There was a trend where older people had longer ears. The difference was about 0.22 mm per year, or about 2.2 mm over 10 years [8].
This result came from measuring different people of different ages at one time. It is not a study that followed the same people for many years. Therefore, we cannot say for sure that "ears grow forever." Heathcote himself speculated that while bones stop growing in adolescence, the cartilage making up the ear might continue to grow slowly [9]. However, this is a guess, and the mechanism is not confirmed.
The topic of hearing high-pitched sounds with age is covered in other articles. This article looked at changes in ear "size."
6. An Experiment: Comparing Pitch Changes With an Empty Bottle
You can try this experiment with a long empty bottle (a plastic water bottle works too), water, and a cup. Place your lower lip against the mouth of the bottle and blow air from the corner of your mouth to make a sound. Next, add some water and blow again. Change the amount of water and listen to how the pitch changes.
By changing the amount of water, you can compare the pitch by ear. This is a separate clue from the story about "shorter ear canals ringing at higher pitches" [5]. It is not the same as measuring an ear canal. Still, it is an experience where you can confirm with your own ears that the length of air affects pitch.
If you want to read more, look for a degree thesis from Kanazawa University in Japanese [5]. It shows how ear canal size and resonance pitch change with age. You can trace the numbers in this article through its tables and graphs.