Does hair grow faster after being cut or shaved? It’s one of those urban legend body myth type things that people just keep believing even though it’s pretty well established that it’s not true. BUT… we view things differently here at SPI, and this Smarticle might just help you feel less crazy for buying into this legend. Like a lot of things we talk about, this is more a matter of perception than anything. Let’s find out why.
Okay, to get started, let’s establish that hair does not, in fact, grow faster (or thicker) after being cut or shaved. Hair grows at a pretty constant rate, and if you’ve ever looked into this phenomenon, you’ve surely found lots of supporting evidence to back this claim. And it’s not just a recent discovery. Here’s one source below:
Another common belief is that shaving hair off will cause it to grow back in a darker or coarser form or to grow back faster. It is often reinforced by popular media sourcesw27 and perhaps by people contemplating the quick appearance of stubble on their own body.Strong scientific evidence disproves these claims. As early as 1928, a clinical trial showed that shaving had no effect on hair growth.w28 More recent studies confirm that shaving does not affect the thickness or rate of hair regrowth.w29 w30 In addition, shaving removes the dead portion of hair, not the living section lying below the skin’s surface, so it is unlikely to affect the rate or type of growth.w26
–Medical Myths, Rachel C. Vreeman and Aaron E. Carroll, BMJ
And there’s no shortage of supporting claims, if you want to dig further. That same article as linked above shares some of the rational, medical reasons for this myth:
Shaved hair lacks the finer taper seen at the ends of unshaven hair, giving an impression of coarseness.w31 Similarly, the new hair has not yet been lightened by the sun or other chemical exposures, resulting in an appearance that seems darker than existing hair.
Here’s the Mayo Clinic with a similar story:
Shaving facial or body hair gives the hair a blunt tip. The tip might feel coarse or “stubbly” for a time as it grows out. During this phase, the hair might be more noticeable and perhaps appear darker or thicker — but it’s not.
-Dr. Lawrence E. Gibson, Mayo Clinic
So why is this idea so sticky? Well, there are several reasons, some medical, that you can apparently find in a lot of places, and one mathematical, that I’d like to believe I thought of first. At least, I thought of it without reading it elsewhere, and that makes me proud. Don’t ruin my moment, okay?
To review: medically, we’ve established that hair does, in fact, grow back at a constant rate. It may appear to be growing faster because of the taper, color, and bluntness of the shorter hair. Now let’s jump into the mathematical side I promised you. Don’t worry if you’re not a graph-type person. It’ll be explained below.
First, let’s plot a graph of hair length. We’ll assume that hair grows at 1 millimeter per day for 25 days (so from 0 mm up to 25 mm — about an inch). We’ll see that it’s linear, because it’s growing at a constant speed. 1 millimeter per day, every day, from the day after it’s shaved to the last day of the month.
Now, here’s where it gets interesting. Using the very same lengths and growth rates, we’ll plot the daily growth percentage. In other words, rather than how much your hair grew in terms of length (millimeters), what you’re looking at below is how long it is compared to the previous day.
Now we’ve got this hockey-stick style graph. Cool, but what does it mean?
It means that on day one, the hair on your stubly face, legs, or whatever, is infinitely longer than it was yesterday. Divide 1 by really tiny numbers just above 0 and you get close to infinity.
But infinity is a hard concept for pretty much everybody, so let’s move a few days ahead. Day 2, your hair is 2 mm long, versus 1 mm yesterday. It’s grown 100% — double its length — in a day. That’s huge! But that enormous percentage growth rate dwindles pretty fast. Day 3, it’s 50% increase — 3 mm versus 2 mm. By day 10, it’s 11%. By day 20, it’s 5%, and it just keeps getting lower.
This means that you notice the growth more in the early stages, because relative to the existing length, starting at 0, the growth is enormous! If you wake up and your bank account doubled (100% increase), you’d notice it much faster than if you logged on to see it had grown by 1%.
Now, because we can, let’s plot these together. And let’s call “Hair Growth Rate” something more useful, so we get a clear picture of what we’re experiencing.
And there you have it. For the first few days after you shave or get a haircut, it’s suuuuper easy to notice, because the relative growth as a percentage is enormous. A few days in, and you’re back into normal, non-noticeable territory.
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