The ways human bodies develop in the womb and continue growing are fascinating - and more than a little gross, too. But that growth has to end somewhere, right? After all, if every body part kept growing, the billions of people on Earth would run out of room to live.
What parts of your body continue to grow? And are there body parts that never grow at all? There are plenty of misconceptions about body parts that keep growing, like hair, nails, ears, and noses. That's not to mention those other strange parts that seem to exist mainly to mystify scientists. The confusion is understandable. How bodies grow and regenerate over time is complex and nuanced, but it's remarkable, too. Look a little closer, and you'll discover the human body is an impressive piece of engineering.
Babies are born with big eyes. In fact, infants' peepers are so large compared to rest of their features that some people think eyes are fully grown at birth. But according to the American Academy of Opthalmology, that’s not true: "The eyes undergo considerable growth especially during the first two years of life, with a second growth spurt occurring around puberty."
Just how much do the eyes grow? They can be measured with axial length - the distance from the front to the back of the eyeball. Axial length is about 0.6 inches for a newborn, and about 0.9 inches for an adult.
Men with a seemingly permanent five o’clock shadow might argue that hair never stops growing. Anyone with unwanted bald patches might say the opposite. So who’s correct? It depends.
Hair, wanted or unwanted, grows in phases on various parts of the body at a rate of about six inches per year. The portion of hair that you see is actually dead hair cells. Once hair reaches the end of a phase, it falls out or breaks off, and follicles send out new cells.
According to the American Academy of Dermatology, it’s normal to lose about 50 to 100 hairs each day. Excessive hair loss might be the result of a medical condition, medications, childbirth, hormone changes, stress, or heredity. But nearly all people undergo hair loss as they get older, and hair growth also slows down considerably with aging (except in the nose and ears, a phenomenon related to hormones).
As people grow older, their noses get bigger, right? That's actually a bit of an illusion, courtesy of gravity. As humans age, the collagen and elastin in the nose that make up cartilage break down. These fibers stretch and sag, appearing longer. Cheeks and lips shrink and lose volume with age as well, which also contributes to the look of a bigger nose.
According to Wojciech Pawlina, "in certain health conditions, the tissue forming the nose (bone, cartilage, connective tissue, etc.) has the capability to be activated and undergo growth. This can be seen in individuals with acromegaly, which can occur with tumor growth in the pituitary gland. With this, the cheekbones are more pronounced, the forehead bulges, the jaw is enlarged, etc." So, your nose can grow - it just probably won't.
The Guinness World Record for the longest female fingernails belongs to Lee Redmond. Her nails reached a length of 28 feet, 4.5 inches in 2008; she started growing them in 1979. So, yes, nails do grow. As people get older, however, nails grow more slowly, and can become dull, brittle, or yellowed.
Nails are surprisingly tough - they'll even come back if you lose one after an injury. A fingernail will take half a year to grow back; a toenail can take a year and a half. Fingernails grow faster on your writing hand, and during summer.
Some people even say that nails keep growing after death, but that’s not true. Skin dehydrates and tightens after death, which makes nails appears to grow.