40 Human Body Facts That’ll Fascinate & Disgust You – Part 6

Like all other organisms, the human mating strategy is part and parcel of our overall survival strategy. In our case, we are extreme “K-specialists,” i.e., we devote a huge amount of investment and resources in our offspring, compared to, say, willows who just scatter their seed to the wind by the millions.

Human females have also developed a strategy of concealed ovulation. The current scientific consensus is that by concealing her ovulation and maintaining a perpetual state of potential sexual readiness, the human female makes it difficult for males to know whether her offspring are theirs. The male counter-strategy is to be at hand as often as possible to prevent cuckoldry. Together, this strategy and counter-strategy promote pair-bonding, monogamy, and dual parental investment, thus maximizing parental investment in offspring.

2. A pimple is an infection. Anaerobic bacteria sometimes colonize a hair follicle and consume the sebum (oily substance) produced by sebaceous glands. They then excrete byproducts that irritate the surrounding area. The resulting inflammatory reaction calls in neutrophils (a type of white blood cell), which just come in and dumps bleach on the bacteria. As neutrophils die, they accumulate and form what we call pus or the “white stuff”. It only has one immediate way out; through the hair follicle to the skin surface. That’s why it exists the way it does.

If left untouched, after a few days the pimple will resolve following absorption back into the body.

3. Facial skin is more prone to blackheads and pimples because the skin on your face has a lot more sebaceous glands than the rest of your body. These glands secrete an oily substance called sebum that moisturizes and protects the skin. These occur in the greatest concentration on the face because one’s face is exposed at all times and it needs more protection.

Facial skin is also incredibly tough, heals very quickly, and has a high blood flow than the rest of the body. Its skin turnover rate is also very fast comparatively. You could drag your face in gravel and it will heal up in a couple of days. A skinned knee will take well over a week to heal.

4. Some birthmarks are blood vessels near the skin (like a capillary hemangioma that grows for several months and then starts to recede). Some birthmarks are just moles, but it makes people feel better to call them birthmarks. Some are basically large freckles that don't mean anything unless you have several of them over a certain size (for example in neurofibromatosis). Some, like the “Mongolian spot” near the butt areas of some babies, show up in a ton of babies and slowly fade with age like the “stork bite” redness behind the neck or the "angel's kiss" between the eyes/forehead.

In the absence of a more sinister condition, they are just plain old unexplained luck or genetics (Mongolian spots appear more in Asians for example).

5. Melanocytes are cells that provide pigment/coloration to our skin and hair in the upper layer of our skin. A mole (or nevus, if we’re getting fancy) is actually considered a “benign tumor” of those melanocytes. ‘Tumor’ just means an abnormal, excessive growth of cells (not cancer), so essentially, some of your melanocytes had some funky things happen with their DNA (damage, random mutation, etc.) that caused them to grow more in clusters as opposed to spreading out across your skin.

The reason why you’re told to check the size, borders, color, etc. of moles is that benign moles and potential melanomas can look very different.

Every human has got the same number of hair follicles on their face and head, give or take, regardless of sex. Your hormones dictate which ones will activate, which is why trans men can grow facial hair. The follicles are there, they’re just not stimulated to grow unless additional testosterone is introduced.

Similarly, a lot of trans women, who were going bald when they were men will start growing a full head of hair when they start reducing testosterone, which revives the dormant follicles and introducing estrogen stimulates the follicles that have never been active. Hair follicles take a very long time to die, and some are never active, to begin with.

7. The dead byproducts of bacteria are called “pyrogens” because they cause (among other things, such as death) fevers. While they aren’t a problem in our day-to-day life (even consuming them wouldn’t affect your health), they are a crucial issue in the medical and surgical fields.

Depyrogenation is the process of cleaning up the germ corpses and the death juices they spit out in their hate. For things like heart surgery scalpels, there will usually be a second step of “Depyrogenation.” This is the process, not of killing bacteria, but of removing the bits left behind so that they don't trigger an immune reaction.

Problems occur when a scalpel with dead bacteria is used in surgery. The immune system works by identifying certain chemical triggers in bacteria, and it has no way of knowing if the lipopolysaccharide hanging around in someone's heart is not part of a living bacteria, but the floating corpses of dead bacteria.

8. The pepper plant evolved its fruits to be eaten by birds and disperse its seeds. Birds are not affected by capsaicin, the chemical compound that makes spicy peppers feel hot. Pepper plants don't even want mammals to eat them because pepper seeds aren’t resilient enough to handle our digestive system, but humans have actually liked the pain and have enjoyed the hot taste associated with peppers. Humans have consequently not only spread peppers globally but have even gone as far as breeding them to be spicier.

FYI, cayenne works well to keep squirrels out of bird seeds. Birds don't mind it but squirrels will avoid it.

9. We humans subconsciously use our own voices to make sure our mouth is making the noises we want it to. This is why hearing yourself speak with a few seconds of delay, completely crashes your brain.

In short, the brain uses nuanced feedback loops, via sound from the ears, to modulate speech, form phonemes, and so forth. When there is a delay in this feedback loop, the brain just isn’t able to figure out what’s wrong but still tries to correct itself. This why singers need foldback speakers or an earpiece when singing with a microphone. Without this, it is difficult for a singer to know if they're singing in tune.

10. Caffeine has no calories, so it doesn’t actually give you a burst of energy. It just feels like it does because it prevents the feeling of being tired.

Caffeine binds to the same place in your brain that adenosine molecules would. Adenosine is what causes your brain to “start feeling sleepy.” Due to caffeine when adenosine can’t bind to those receptors, your brain doesn’t get the “bedtime” signals. The resulting extra adenosine in your bloodstream then triggers your adrenal system to release more adrenaline, which then affects the dopamine system in your brain, which results in you feeling happy/good.

Corona and influenza viruses are single-stranded RNA viruses. Once they get into your cells they start replicating, which your immune system is very good at recognizing and killing. That’s why these kinds of viruses infect once and most of the time they are done.

Herpes on the other hand is a double-stranded DNA virus. It can get into your cells and just sit there not replicating, so it is hard for your immune system to detect it. It will become active and replicate periodically, but then it infects other cells where it will just sit dormant again. So your immune system is playing whack-a-mole, which isn't very effective.

In the case of HIV, it is a retrovirus, so it actually integrates into your cells’ own DNA. You can't get rid of it without killing the host cell, and the cells it primarily infects are T-cells, which are immune cells that are generally tasked with antiviral immunity and it kills the very cells responsible for killing it. It can also hide in other cells that create a reservoir for it to become infectious again, which makes it even more difficult to treat.

12. Alcohol is a depressant, which means it slows the activity of the brain. If someone abuses alcohol over a long period of time, their brain will adapt and create more and more sensitive reactive chemicals to try to retain normal brain function even in the presence of alcohol. This is called tolerance. If the person were to suddenly quit drinking, the alcohol that was inhibiting brain reactions is no longer present, but the overly reactive chemicals are still there, meaning the brain is way more active than it's supposed to be. This is a seizure. It’s similar to overloading a circuit with too much electricity. It burns out and misfires, which can lead to death.

13. When a baby is inside its mother, its lungs are deflated. They’re essentially in a breathed-out half-collapsed state that’s supported by amniotic fluids. When the baby comes out, the sudden change of environment and temperature causes the body to begin its first inhalation. The lungs expand, blood flow to the lungs increases, and the fluid is absorbed. The first breath is raspy because the fluid is still there; but the lungs were never full of it, so the expanding space is filled with fresh air.

The sudden rush and overload on its senses, bright light stinging their eyes that were used to near-total darkness, the rush of sounds closing in and everything else associated with the birthing process totally tires the baby, so they sleep for nearly 24 hours afterward, misleading new parents to think they have got a really easy baby.

14. Traumatic experiences can make the body and brain age faster. Stress leads to higher cortisol which leads to physical aging. This process is so strong that children who experience high levels of stress like violence or trauma in infanthood/early childhood statistically start puberty earlier than their non-traumatized counterparts.

One theory posits that early puberty/aging allows for increased survival in traumatic environments. It grants not just sexual maturity but increased bone density, muscle mass, etc. which basically allows you to become an adult faster to survive.

15. Indigestion, diarrhea, and other stomach issues are common side-effects of strong/broad-spectrum antibiotics because they kill nearly all of the healthy gut bacteria. Some bacteria though can escape due to a combination of factors, some are replenished from the appendix (turns out it is now thought to be a reservoir), and food. Probiotics have been found to be entirely useless in these cases.

In some extreme cases, doctors might recommend stool transplants, where a stool sample is brought in from a “stool bank” which is then transplanted into the patient via enema or an oral capsule.

Armpit sweat glands are known as apocrine sweat glands, and instead of producing just sweat, they also produce a mix of proteins and lipids. The bacteria on your skin love that stuff and eat it up, producing waste products in the process. It's those waste products that cause pungent armpit odor.

There’s a reason why we secrete these oils and proteins in the first place. Hair under our arms and between our legs acts as a dry lubricant. When it isn’t enough (during intense exercise or prolonged walking/running), these secretions help reduce the friction and damage to the skin.

Each person has a unique combination of bacteria on their skin which in turn makes them have a unique smell, kind of like an olfactory fingerprint. Humans still use it to recognize family and friends from everybody else on a subconscious level.

17. There’s a reason you feel tired by just traveling in a vehicle and doing nothing else. There is lots of data on the “stressors of flight” (many of these stressors are also present in automobiles). As the vehicle moves, the sway and direction change causes you to make micro-adjustments to keep yourself upright. These micro-movements cause your muscles to be continuously working (even if you don't realize it).

Studies done by the US Airforce reports that consistent exposure to aircraft vibrations can lead to fatigue and an increased chance of health problems.

18. Human skin is amazingly resilient and has a shockingly high tensile strength, which is roughly 27 MPa (MegaPascals), whereas High-Density Polyethylene (milk jug plastic) is only around 15 MPa and ABS (LEGO plastic) is only about 50% stronger at 40 MPa. When someone gets big rapidly like during puberty, muscle growth, or pregnancy; the skin won’t tear but this will only result in stretch marks.

19. Estrogen alone is not solely responsible for breast development and size. It is a complex interaction between genetics and several different hormones which includes steroid hormones, estrogen and progesterone, growth hormone, insulin-like growth factor 1, and prolactin.

The best (but not the only) predictor of your breast size will be your other female relatives. Having high estrogen, just like having high testosterone, is not even necessarily a good thing. It’s associated with an increased risk of depression, anxiety, hair loss, thyroid disease, heart attack, stroke, blood clots, breast cancer, and ovarian cancer. It also doesn’t make you more likely to conceive as it causes decreased sex drive and irregular periods.

20. Children tend to be more sensitive to bitterness, which is apparent in foods like broccoli and Brussels sprouts. This is an evolved defense mechanism because poisons are often bitter-tasting. As we grow, we learn which foods are poisonous and which aren't, so we don't need the same sensitivity and through evolutionary pressure, we lose the sensitivity over time.

When you complete a quick, strenuous exercise, some excess hemoglobin is released from your blood cells into the lungs due to increased heart rate and the resulting increased blood pressure, which is then carried to your mouth during an exhale. Hemoglobin is made up of iron. This is why you get a metallic blood-like taste when you thoroughly exhaust yourself.

22. Some viruses are structured in a way that when antibodies necessary to disable them are activated, they also become harmful to the human body itself. Many forms of kidney failure in the young are triggered by the immune reaction to streptococcus. Many forms of type I juvenile diabetes are thought to be caused by the body’s immune response to a viral infection. This is in fact the mechanism presumed for a number of autoimmune diseases that appear to be precipitated by a viral illness.

23. The thymus is an important immunological gland located in your upper chest that produces T cells. These are important white blood cells of the immune system. This gland begins to deteriorate after you hit puberty, though it doesn't fully degrade until old age at which point it essentially becomes non-existent. This is the reason why with aging it becomes harder to heal from illnesses and why young kids tend to bounce back faster after illnesses.

Basically, our immune system starts to shut down as we get older because we’re simply not meant to live so long. There's no biological reason to live very long, just sentimental reason.

24. When you have a “gut feeling” it’s the subconscious part of your brain triggering a mild fight or flight response. This happens when the always watching and listening subconscious part of your brain notices something that the conscious part of the brain was too distracted to notice. The hypothalamus then signals your adrenal glands to release adrenaline to give your body some extra strength, so that you can either run faster or fight harder.

Among other things, adrenaline will cause your bowels to contract and your blood vessels to expand. This is what that stomach sensation basically is and why some people will literally sh*t themselves during a high-stress situation.

It is also worthwhile to point out that the gut feeling can be sometimes completely wrong and you can see extreme examples of this in people with anxiety disorders, who experience way more “false positive” alarms.

25. Humans are insanely good at seeing patterns. We see patterns in things we're not even supposed to, and we do it all the time. It's why we can see animals in clouds and faces of dead celebrities in malformed potato chips.

It's not just visual patterns we’re good at. One really interesting example of this is the ‘red flag’ phenomenon, where you just get a bad feeling about someone, even if you haven’t actually seen them do anything that warrants caution. In many cases, this red flag turns out to be right all along. That’s the pattern recognition in our brains going off. There may have been just something about the person that set off your internal alarms. Perhaps maybe you’ve subconsciously noticed similar expressions, speech patterns, behaviors, etc. in people who did actually turn out to be bad in the past. Your brain keeps extensive records of that sort of thing whether you're aware of it or not.