I’ve often been told that this isn’t actually true but I can’t help but feel that it does happen. Until recently I hadn’t shaved for about a year, maybe two. Now I feel like it’s growing back quicker than what it did the last time (after shaving on a more regular basis).
It doesn't, it's a perception bias caused by a few different things like others here have mentioned, but also freshly grown hair tends to be thicker, then tapers off as it grows, so it SEEMS thicker.
If youre in your 20s or 30s, its entirely possible your beard grew back faster compared to a year or two ago. But thats because of getting older and stuff like that. Your beard doesnt grow faster just because you shaved recently.
The rate at which your hairs emerge from their follicles is constant, but the rate of increase of the total length of the hairs slows down and eventually stops because the hairs naturally wear down over time.
Imagine that your hair is like pasta being extruded into water, and that it slowly dissolves over time. The more time the pasta has been in the water, the faster it dissolves—and it eventually reaches an equilibrium length where the tip is dissolving as fast as the other end is being extruded. But if you cut off the pasta at the extruder and time the new pasta coming out, you’ll measure the full extrusion speed instead of the extrusion speed minus the length-dependent dissolution rate.
It doesn't. The growth is the same. The perceived difference is because the ends of the hair are straight and uniform rather than all raggedy. People have been asking this for years and have been hearing this answer for years but for some reason keep asking the same question over and over.
I don't believe it actually does grow back faster, it just seems that way. The first inch or so gives the impression of growing back faster because the hairs are thicker at the base so they're more visible and less prone to breakage.
AFAIK, apart from drugs, only stress and malnutrition affects hair growth speed. Stress can increase cortisol levels, which can lead to faster hair growth, but chronic stress and malnutrition may lead to hair loss.
As a transgender woman, I have personally experienced that hormone replacement therapy (HRT) -- which includes estrogen as well as testosterone blockers -- slowed down my facial hair growth and thinned out of my facial hair. So testosterone levels play a small part in facial hair growth. However, I doubt that the levels within a cisgender male would vary enough to cause any significant changes.
It's probably just that there's a fair bit of hair growth that happens before the hairs reach the surface of your skin, like a millimeter or two. When you shave, it only has to grow back enough to pop out over the surface of the skin. If you were to pluck a hair with a pair of tweezers, it would take at least a couple of weeks to grow back. I have done exactly that many times, so at least for me that's the time frame.