ELI5: Is letting wounds 'breathe' a thing, if so, what purpose does it serve?

I’m a nurse and have taken a number of courses on wound dressing and healing. Here’s what I can quickly write out for you.

The goal of wound care is moist wound healing. If wounds are draining plenty of blood/pus/serous drainage and it isn’t being removed from the wound by an absorbent dressing, the tissue can become macerated and will appear white. It’s too wet, the tissue is swollen with water. This is bad for wound healing. This is maybe where people got the idea of letting a wound “breathe” to dry up some of the excess moisture.

However, letting it dry out completely is not ideal either.

Natural healing involves developing a scab, a dry cover for the wound. However, if the wound were instead moist (not wet), you would have faster migration of immune cells, new cells, growth factors, etc. as they can move through a moist environment easier. This is what topicals like polysporin (besides the Abx) help to achieve. Petroleum products will moisturize without macerating.

And the other question everyone asks: should I use peroxide to clean it? no. maybe. Here’s the thing. You can clean a wound very well with water or saline (although who has saline at home). Many wounds wash themselves out by bleeding! Peroxide will kill bacteria, but it also hurts exposed skin cells/other tissue, and that can slow healing. The surface of your skin is mostly keratin and peroxide won’t affect intact skin, but when it’s cut, the deeper layers can be affected. Basically, don’t peroxide every wound, but something like a cat bite, go for it.

*edit: I’m aware now of how many people have saline. I pour like half a liter over new wounds, so I’m not sure people have that much contact solution. I have 25/20 vision privilege so am unaware. Yes, you should see a doctor quickly for cat bites. I’ve seen people need strong antibiotics 4x a day to avoid death from cat bites. Go to ER NOW if your wound starts streaking red up your limb. Helpful to outline areas of redness with a pen and the time you marked it to show how it’s progressing.

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ELI5: When sending a letter abroad, how does the receiving country's mail service get paid for their work?

There is a global unified postal service body called the Universal Postal Union . The Union creates a framework and standards so that ALL countries can exchange mail freely without forming individual contracts with every other country.

When one pays for the postage for international mail, a portion of the money goes to the home country’s postal service and a portion goes to the destination’s postal service. The portion of money exchanged depends on how much mail (in weight) each country is exchanging. This is set up so that the destination country receives money for delivering the postage. Countries that receive more mail annually get less money per kilogram of mail.

The fee paid to the destination county is called a terminal due.

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ELI5: why do you see weird patterns when you close your eyes and apply pressure onto them?

This phenomenon is called phosphene.

When light hits the cells in the eye, these cells send a signal to the brain to give an image of what is seen. These cells are called photoreceptor cells, and their main means of activation is when a photon of light hits them. Another way to activate them is via mechanical stimulation (aka applying pressure to they eyes). When you apply mechanical stimulation, the subsequent activation of the cells will be random (not patterned), and when this signal is transmitted to the brain areas that are responsible for generating an image, you will see weird patterns instead of the normal images that would be generated by photon-induced stimulation.

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ELI5: What exactly did John Oliver do in the latest episode of Last Week Tonight by forgiving $15 million in medical debt?

Whenever you take out a loan or get a service that you don’t pay for in advance, you owe someone money. If you don’t pay, they chase you down looking to get their money. For many of these people who are owed money, they want to spend their time performing services for people, not chasing down delinquent payers. So for a fraction of the total price of the debt, they sell the right to collect the money to some third party. That way they get some of their money back (more than they would without a bunch more effort chasing down the people who haven’t been paying).

So now the third party who specializes in chasing these people down will try to find the people who haven’t paid and get them to pay. What John Oliver did was buy the right to collect these debts, just like these third parties do, but then forgive the debts- tell the people who owe money that they don’t have to pay him back.

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ELI5: Why is menthol "cold"?

The people saying it’s because of evaporative cooling are wrong. Menthol’s boiling point is 212 Celsius, much warmer than your body.

Menthol isn’t really cold, it just tricks your body into thinking it is. There’s a type of nerve cell that responds to things like temperature, pressure, pH, etc. Some of these cells have what’s called a TRPM8 receptor on their surface. When menthol comes into contact with a TRPM8 receptor it binds to it, which makes the affected cell open an ion channel that admits sodium and calcium ions into the cell. This in turn causes the nerve cell to send a signal to the brain that the brain interprets as coldness. A similar receptor, TRPV1, is why the capsaicin in hot peppers feels ‘hot’.

Basically, menthol binds to a receptor on certain temperature-sensitive nerve cells, causing them to fire, and your brain interprets this nervous activity as coldness.

EDIT: Okay, evaporative cooling probably does have something to do with it, and it isn’t necessary for a substance to reach it’s boiling point to evaporate. However, I’m willing to bet that the cooling sensation is caused overwhelmingly by TRPV8 activation.

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ELI5: How do people solve rubik`s cubes in <10 seconds?

Rubik’s cubes are actually solved with a formula, or simple set of rules. Once you know those rules by heart, it just becomes a matter of applying them in the most efficient way (to minimize the number of moves required) and then moving your hands very, very quickly. Those with good memories for images can actually look at the cube once then put on a blindfold and solve it from memory.

Fun fact - every possible (valid) permutation of a Rubik’s Cube has a solution which is no larger than 20 moves. This is called “God’s Number” and it took about 30 years to determine this number. Over 99% of all possible permutations require 16-19 moves to solve.

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ELI5: When you go on a roller coaster or drive fast down a hill, why do you get that stomach drop feeling? What is actually happening inside your body that causes the feeling?

“The honest answer is that no one knows with absolute certainty,” said Dr. Brad Sagura, a surgeon at University of Minnesota’s Amplatz Children’s Hospital.

“There’s a cast network of nerve connections within the body, handling messages between the spinal cord, the brain and other structures,” Sagura said.

When you hit the peak of a roller coaster and start dropping so quickly, things inside start to shift around.

“The liver and spleen are relatively secured by suspensory ligaments,” Sagura said. “But the intestines themselves are relatively mobile. While your body is secured by your seat belt, the organs are free to move about by some extent. That contributes to the free-fall floating sensation that either calls us back for more, or has us running to get sick from nausea.”

The movement isn’t only the movement of the organs, it is also the movement of what’s inside the organs.

“The intestines, the stomach, they hold liquid,” Sagura said. “The bladder; the same thing. “It’s relatively fixed, but the fluid within those structures probably plays a role in that sudden drop.”

Sagura said there’s no long-term danger from your organs slightly shifting around. They go back to where they started. But the movement is enough for your nerves to notice that something’s happening, he said.

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