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.
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).
13Skin Moles, why?
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.
15What Happens to Dead Bacteria?
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.
16Human Love For Peppers
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.
17Delayed Auditory Feedback
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.
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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.
19Corona vs HIV Viruses
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.
20Alcohol Withdrawal Death
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.