When I was little I had pretty straight hair. When I started the earliest stages of puberty- around 3rd grade or so- my hair got super curly. It stayed curly until I got pregnant with my daughter. Exhibit 1:
So what happened? Why did my hair change? I didn’t know, but was curious and went in search of answers.
First I asked around- I found a few other moms whose hair had gotten curlier or straighter during/after being pregnant. Since they were all scientists, they could speculate why, but nobody knew for sure.
A quick Google search turned up tons on info on post-partum hair loss, and articles about how thick and full hair can get during pregnancy, but nothing about a change in texture. Therefore- a more in depth Google search.
Here are my findings…
Most of what I knew about hair growth, I actually learned from mice. Hair growth is cyclical, with two primary phases: anangen (when the follicle is actively growing hair), and telogen (when the follicle is resting and sheds the hair it had been growing). There are a variety of mouse mutants that have long hair- thanks to changes in genes that prolong the anangen phase. The length of the cycles vary depending on the location of the hair and are controlled by a variety of growth factors and hormones.
Normally the majority of the hairs on your head are in anagen (about 90%), with 10% in telogen. So you lose hair everyday, but since it’s the minority of hairs on your head, it’s not noticeable.
While you’re pregnant, estrogen and other hormones prolong the anagen phase, meaning you lose fewer hairs and most women report thicker, fuller hair. Once you give birth, your hormone levels fluctuate and the follicles on your scalp that had been kept in anagen, transition to telogen and you shed lots of hair at once. That process is called post-partum alopecia and is a form of telogen effluvium.
Telogen effluvium could explain how my curly hairs fell out, but it doesn’t explain why the hairs that grew back weren’t curly. So, what makes hair curly?
Turns out, the shape of your hair is due to the actual shape of the follicle from which it grows. This post by Anne Tecklenburg at Stanford was really helpful at explaining hair texture . The take home message:
So did my follicles change their shape after I was pregnant? Were hormones responsible for my hair getting curlier at puberty and less curly during pregnancy?
It is known that estrogen strongly influences hair growth (see here), and we know that estrogen levels fluctuate during and after pregnancy and birth. However, the exact molecular mechanisms responsible for the change in hair texture during pregnancy may not be known- or are an area of active research. This great piece on NPR addresses just that possibility: A Hair Mystery: Curly Hair Gone Straight.
The conclusion from all this- while not definitive- is that yes, hormonal changes during pregnancy can alter the texture of hair, most likely by changing the shape of the hair follicle.
A coworker of mine had her hair go from stick straight to very curly with her first pregnancy, and from very curly to wavy with her second. As I’m now almost 19 weeks through this second pregnancy, and hair grows about 1.25 centimeters per month, I have about 5.5 centimeters of hair that has grown since I got pregnant. While I have noticed less hair loss, so far, I don’t see it getting curlier, if anything it’s getting even straighter.
I’ll be sure to update when my hair growth normalized post-pregnancy.
WebMD- Telogen effluvium
Standford’s Ask a Geneticist- Hair Biology
Wikipedia- Hair Follicle