The first weeks and months of a baby’s life are full of big changes. But
what new parents may not have expected are the tiny hairs left on their
newborn’s mattress. After a few months, their baby’s once-full head of hair has
become thin and patchy — or nearly bald.
Fortunately, infant hair loss is rarely a concern. A fetus starts
growing hair during the first trimester. But whether an infant is born with a
layer of fuzz or a thick mop, all lose at least some hair. In fact, hair loss
simply means an infant is making the huge adjustment to life outside the womb.
On an adult’s head, each strand of hair goes through a phase when it’s
growing and when it’s not — and when hair isn’t growing, it can also shed. At
any given time, only a small percentage of your hair is in this latter stage,
and only about 50 to 100 strands are lost per day. Not so for a newborn.
“Big hormonal shifts happen in a baby’s body after they are born, which can
cause all of their hairs to enter the resting phase at the same time,”
explained Sage Timberline, a pediatrician at the University of California,
Davis, Children’s Hospital in Sacramento, California. That means all of a
baby’s hair can shed at once.
Both mother and baby undergo huge hormonal shifts during labor, which
is necessary for a successful birth. The onset of labor alerts a baby’s body to
start producing hormones that are crucial for life outside the womb. Some
hormones help the baby’s arteries and veins develop, ensuring that the organs
receive ample blood during labor and after the umbilical cord is cut.
One hormone, called cortisol, helps babies’ lungs mature,
enabling them to take their first breath, Timberline said. It also helps the baby’s
body produce its own energy and heat. In adults, cortisol plays a role in a
vast array of physiological functions, from regulating metabolism to triggering
your “fight-or-flight” response. It’s considered the stress hormone, and during
times of stress, cortisol helps direct energy toward vital functions and away
from less important tasks.
“Labor puts a good kind of stress on a baby,” Timberline said. The stress
triggers cortisol production, which channels energy toward the developmental
changes crucial for survival — and away from nonessential functions such as
hair growth.
Hair today, gone tomorrow
After birth, all of a baby’s hair stays in the resting phase until more
resources become available. Hair usually starts to shed at 8 to 12 weeks of
age, and begins to grow back at around 3 to 7 months. But it’s not until around
2 years of age that thicker hair emerges. The specific timing and pattern of
hair loss and growth depends on a number of factors, including sex, ethnicity,
genetics, the conditions of birth (premature, early or late; or vaginally
or by cesarean section), and a baby’s nutrition.
And no, what you may have heard about shaving a baby’s head to allow hair
to grow back thicker isn’t true. The ends of a baby’s hair are tapered, and
cutting them just leaves them truncated and temporarily looking darker and
thicker.
In fact, the number and location of individual hair follicles are
genetically determined, said Katie Ellgass, a pediatrician at Stanford
Children’s Health Altos Pediatric Associates in Los Altos, California. Once
born, a baby doesn’t form any new follicles.
A baby’s hair color and texture can also change several times during the
first few months or years. But it’s hard to predict how and when, Timberline
said. “All we can do is enjoy each hairstyle while it lasts,” she said, “and
don’t get too attached!”
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