Remember a few months ago when I looked like this?

That was because I was doing chemotherapy for Hodgkin Lymphoma, but still coming in to record SciShow videos because I LOVE MY JOB. But before that, I Iooked like this, look at him, he’s so young and free and not overly concerned with mortality.

But now I look like this! Older and wiser, and more anxious and also… MY HAIR IS CURLY??? Why is it curly?

It’s never been curly! And this is a common thing! So common that it has a name… chemo curls!

So we looked into it because that’s what we do around here. And you know what we found out? Nobody is studying this!

We only barely understand why chemo changes your hair, and nobody seems to even care! In this video, I’m going to talk about what we do know about chemo curls, and hopefully convince some of you out there why it’s worth understanding them a little better. [♪ INTRO] So, to start off, fully or partially losing your hair during chemo is formally referred to as chemotherapy-induced alopecia. Chemo curls don’t seem to have their own formal name, but many studies of alopecia have noted changes to hair texture or hair color.

Now, changes to your hair might seem like small potatoes compared to, you know, cancer, but don’t write it off so quickly. Hair is a pretty important element of human culture. Our hair can be a reflection of our age, our culture, even our politics or religious affiliations.

So losing it or having it change can cause real distress! But, also, it would just be great to understand chemo curls because it’s just cool to know things. Now, it’s hard to even say how many patients get chemo curls.

The rate of alopecia, or hair falling out, tends to vary depending on the exact therapy and dose, but it’s generally around 65%. With chemo curls in particular, the estimate you’ll most often see is around 65% of patients have changes to their hair texture. Though – as a quick tangent here – this number around texture changes might be more of a very rough guess.

Because this is quoted in a lot of papers. But if you actually chase down the citation and read where it comes from, it’s from a single, one-quarter-page letter to the editor of one doctor’s observation of 35 patients… in 1988. Now, that person wasn’t doing anything wrong, pointing out that you noticed something interesting is where science begins.

But there have been, like, maybe two studies since then? And people seem really unbothered about citing this thing from 1988 given the, like, let’s say…lack of statistical power. Scientists.

I’m talking to you right now. I know we can do better than 35 people 36 years ago. One of you has to have access to a large patient population.

Design the survey! Start asking people! I want to know more about this!!!

Now, as for why this happens, it has to do with how chemo works in the first place, as well as a strange quirk about how hairs grow and recover from damage. So, generally, chemotherapy works by targeting rapidly dividing cells in our bodies. And that’s good!

Cells dividing willy-nilly is one of the things that makes cancer cancer. And for much of our body, once we reach adulthood, our cells don’t actually divide that much. Skeletal muscle cells straight up don’t divide once they’re mature and bound together.

So chemo won’t really affect those parts of our bodies. Unfortunately, there are a few places where we depend on rapidly dividing cells, like inside the gastrointestinal tract and in the hair follicles. In fact, hair follicles are usually proliferating faster than even a fairly nasty tumor.

We won’t go into an exhaustive explanation of hair biology right now, because we would need a couple hours. What’s important is that in each hair follicle, there’s a kind of central bulb of stem cells that divide and kind of extrude daughter cells upwards, like an infinite toothpaste tube. These cells come together with other components to actually form the hair.

That’s right… each one of your hairs is just a really long stack of dead cells. Hair follicles go through multiple stages where they grow a hair, shed it, and then rest for a bit. The growth phase is referred to as anagen.

Dividing so much is a lot of work for those cells, so the hair follicle is surrounded by capillaries to provide easy access to nutrients. Unfortunately, all of this makes the hair cells sensitive to anything circulating in the blood, like changes to hormone or nutrient levels. Or chemotherapy.

Exactly how chemotherapy kills cells depends on the kind of treatment, but it’s often due to DNA damage activating a protein called p53, which is kind of like a “self-destruct” switch for the cell. If this happens to enough of the hair cells in the follicle, it can either slow down or completely shut off hair production. This seems to be the origin of alopecia… and of chemo curls.

Now, this is where we get into the less-studied realm, so I can’t tell you all the specifics. But we know that a couple of different things affect hair texture normally, like the angle of how the hair follicle sits in the scalp, how evenly the cells are arranged in there, the shape of the hair itself, and even the distribution of proteins throughout the hair. It seems like any or all of these might be affected in that chemo-based cell death.

It can even cause changes in hair color if pigment production is affected. This all happens under the skin of your scalp, so the effect might not be obvious right away, but as the hair regrows, you get to see what you spun on the chemo curls wheel of fortune. And actually there’s kind of a weird, counter-intuitive thing here.

Because gentler chemo, not rougher, might be responsible for chemo curls. When the chemo is relatively gentle, the active hair follicles become damaged, but don’t leave their actively growing anagen phase. They are damaged, though, which results in changes to the hair, like maybe the signature chemo curls.

But with really strong chemo, it can completely shut down growth and force hair follicles into their rest phase. When production does start up again, the hair follicles effectively have to start from zero… regrowing comparatively normal hair! That’s what we think, anyway, but again – more studies would be nice.

Now, chemo curls are usually temporary as hair follicles recover. But chemo is not the only treatment that exists for cancer. What about newer treatments that are more targeted than traditional chemo?

Do they cause chemo curls? In general the answer still seems to be yes, but not as much so. But again, this is also understudied.

For example, we found one study that showed breast cancer patients who received tamoxifen experienced less hair damage compared to those on chemo. Tamoxifen starves cells of estrogen, which is a hormone that breast cancer cells usually need a lot of, but which isn’t as directly involved in hair growth. So that does make sense.

Probably – although hair does like a bit of estrogen which reinforces that we need to study this more! So this is all interesting, but why is it important? After all, it’s just hair.

And if the patient’s cured, shouldn’t they just suck it up and stop being so vain? No, obviously not, and we have numbers to back this up. According to one study, anxiety around how chemo might affect their appearance drove 8% of eligible patients to reject chemotherapy.

Understanding this stuff better could save lives! Like I said before, how we look, including how our hair looks, can be hugely important for people’s self-identity, to the point of influencing medical choices. Though, of course, the loss of the hair is a bigger deal than what it looks like when it eventually comes back.

And that’s a huge relief to a lot of patients: the hair comes back! And maybe it’s even a little exciting that it might come back different. And you get…just like, a very expensive perm.

So studying things like why our hair changes during chemotherapy can be important. Knowing more might help us tailor treatments to avoid unwanted changes, or at least to make us better at anticipating them. Doctors really should not underestimate how important quality-of-life concerns are in terms of a patient’s health.

But also, maybe it’s important to remember that with cancer, or any big health thing, really, the people who go through it don’t experience it in the way that doctors or scientists may think about it. I had this experience a bunch of times, like receiving the “good news” that I had “only” a 5% chance of dying in the next five years. That did not sound, like, as rosy to me as it did to my oncologist!

We don’t see numbers on a chart. We see it and feel it in our bodies – the weird inexplicable pains, the days we feel worn out for no reason, the little changes out of nowhere. Constantly worrying about infection or other serious complications.

So when another change pops up, it can add more anxiety on top of an already incredibly anxious time. Or, you can be like me, kinda pleased to find out what it’s like to live the curly hair life…at least for a bit. I’m gonna keep growing it.

See what happens up there. What I can tell you so far: I think it’s better. It’s just a lot more work!

But I have always found that knowing more helped me feel better about what was happening to my body, and it’s weird that I, a science guy, am constantly being asked why my hair is curly now and I have to say, “Y’know… it might have something to do with the shape of the follicle, or the proteins being produced, or how the cells are arranged in there as they heal, but as of now… we don’t really know.” Now, before you all go, I want to direct your attention to another one of our videos. We recently finished one of the most ambitious videos SciShow has ever attempted. It's on the bizarre future of telescopes… which are pretty ambitious themselves.

I’m talking about a telescope that spans two continents, using a lunar crater as a telescope dish, and much more. We even had a special guest host: Astro Alexandra! If you’re looking for something to watch next, it’s nice and long and would be perfect for watching with a cup of tea… or putting on while you do the dishes… or looping all night while you sleep… Just suggestions.

My point is, it’s really good and you will like it, so go check it out. [♪ OUTRO]