Common health mysteries solved: why do paper cuts hurt so much?

Posted: 10:18 AM, Mar 11, 2013
Updated: 2013-03-11 10:18:50-04

Why do paper cuts hurt so much? Why do onions make you cry? Does celery really count as “negative calories”?  They’re common health mysteries that make you go, “Hmmm.”  Dr. Yael Vernado, of, stopped by to solve them.

Why do paper cuts hurt so much?

There are a couple of reasons why paper cuts are so painful and irritating.

  • Your hands and fingers are great sensors and guides for your body.  They are packed with nerve fibers called nociceptors.  These fibers can sense temperature, pressure and pain, and there are more of them per square inch in your hands and fingers than most other parts of your body.
  • Next reason?  The type of cut.  Sure a paper cut is much better than a deeper cut, but because it’s shallow and not as clean a cut, it’s not going to clot (it may not even bleed much if at all) which means that that cut is exposing nerves to the air much more – which means more “ouch”!
  • Also, you simply use your hands and fingers more than most parts of your body on a daily if not every-minute basis.  Couple that with the density of sensors in those areas and you’re in for an irritating post-paper cut feeling.

Does celery really count as “negative calories”?

If you’ve ever been on a diet – or had someone in your family who was – you may have heard them talk about how they’re sticking to celery for snacking because of it’s negative calories.  So is this fact or fiction?

  • First let’s clear up what they mean by negative calories.  It’s what people say when they mean that the food takes more calories to eat and process than it actually has in a serving.
  • In truth “negative calorie” foods don’t exist because of the definition of what a calorie actually is and how it works.  (Calories wasted while processing foods are already considered in calculating the Thermic Effect of Food (TEF) meaning the amount of energy it takes to metabolize the food.  TEF usually wastes about 10% to 20% of calories which means a 10-calorie stalk of celery wastes 2 calories to deliver 8.   Not a major impact on your diet or “points” to begin with.)  Even if you did end up spending more calories than you took in the effect would be too small to even measure!
  • At the end of the day “free foods” and “negative calories” are often used by dieting programs and magazines to make you feel better about eating vegetables that are made up mostly of water and fiber.
  • Basically – if you substitute celery and cucumbers and other “negative calorie foods” for your usual cookies and cakes, sure you’ll lose weight but you aren’t going to drop dress sizes by chewing celery all day long!

Why do onions make you cry?

We’ve all experienced the moment when we cut into an onion and within seconds our eyes well up and we begin to cry – I fact It only takes about 30 seconds to start crying after you make the first cut, that’s the time needed for syn-propanethial-S-oxide formation to peak.  Syn what?  Here we go – get your science hat on!

  • When you cut into an onion, its ruptured cells release all sorts of goodies, like enzymes and amino acid sulfoxides. The enzymes breaks the amino acid sulfoxides into down into sulfenic acids.
  • These acids are unstable and spontaneously rearrange (into thiosulfinates) which produce a pungent odor and the acids are also converted by into a gas called syn-propanethial-S-oxide, also known as the Lachrymatory (Crying) Factor.
  • This “Crying Factor” (Syn-propanethial-S-oxide) moves through the air and reaches our eyes. The first part of the eye it meets, the cornea, is filled with fibers that lead to the lachrymal (tear) glands. When Crying Factor (syn-propanethial-S-oxide) is detected, all the fibers in the cornea start firing away and tell the glands to wash the irritant away.
  • Before you know it your eyes automatically start blinking and producing tears, which flushes the irritant away.
  • Another problem when cutting onions?  Our reaction to our tearing, burning eyes is to rub them, which only makes things worse since our hands also have some syn-propanethial-S-oxide – the Crying Factor –  on them.
  • How to prevent this problem?  Some people actually wear “onion cutting goggles” to minimize this effect!  You can also refrigerate your onion before cutting it which slows the chemical reactions that lead to your tears!

Is “breaking the seal” when you have to use the bathroom an actual medical phenomenon?

Now this is a phrase that gets popular when you are in college or “of age” to drink and refers to the fact that if, when drinking, you go to the bathroom and “break the seal” you will then have to go to the bathroom quite frequently.

  • Part of what makes you pee so much while boozing is that alcohol inhibits antidiuretic hormone or ADH. ADH is made in the part of the brain called the hypothalamus, and then stored and released from the pituitary gland at the base of the brain. Its job is to conserve water in the body by reducing its loss via your urine.
  • Alcohol messes that all up and blocks certain nerve channels that help get ADH secreting out into your system. Without ADH conserving water, the kidneys don’t reabsorb water as easily and excess water winds up getting dumped into urine to leave the body.
  • With alcohol keeping ADH from doing its job, you produce a lot more water-diluted urine, which fills the bladder quickly and makes you have to pee more often.
  • So, there’s really no seal to break and in fact the moment  you took your first drink and started suppressing your ADH, was when that imaginary seal started breaking!
  • ALSO, alcoholic beverages can be a bladder irritant for many people and the carbonation in drinks like beer and champagne can cause gas and pressure that contribute to that irritation. As your bladder fills up after that initial pee, all that irritation can create a very strong urge to pee some more and make your bladder feel fuller than it really is, sending you running to the bathroom over and over again throughout the night.
  • Thus the legendary seal was and is broken in your mind, but it’s really just your body dealing with your alcohol intake!

Why do beans give you gas?

This is a popular question doctors receive.  Why is it that we don’t get gas when we eat things like rice or pancakes but we do get it with beans (not to mention cabbage, onions and other gas-inducing foods).

  • The answer lies in sugars believe it or not!  These foods are naturally sweetened by a family of sugars called oligosaccharides. These sugars are big molecules that your body cannot break down and that are too big to slip into your body through the lining of the small intestine.
  • This means they move through the GI Tract and into the large intestine still intact and bearing valuable nutrients.  Then the bacteria in the large intestines go at them and as the bacteria chows down on the sugars they let out gas in return
  • Eventually this gas has to be let out of your body and it is via you passing gas.
  • Bonus info: why does your gas smell?  In truth the gas you produce in your intestines is actually odorless!  Sulfur is the substance that causes gas to have odor. But eating foods that are high in sulfur, such as garlic, onions, leeks, broccoli, cauliflower, cabbage and Brussels sprouts, can cause foul-smelling gas.

Why do spicy foods make my nose run?

You know how it goes – you bite into something spicy like a chili pepper, wasabi or hot curries and your nose begins to run – what’s up with that?

The answer can be given in one word: Capsaicin.

  • Capsaicin is the chemical found concentrated in the tissue of peppers (and allyl isothiocyanate is an oil contained in plants like mustard and radishes including horseradish).
  • Plants use both of these chemicals as biological weapons against predatory animals.  But when we consume them they act as an irritant, produce a burning sensation and when ingested they cause your mucous membranes to become inflamed and go into defense mode. This means producing mucous to them out of your respiratory system by removing them via the nasal passage.
  • Some more important scoop?  Some people think that spicy foods clear their nasal passages when they have a cold and thought it may cause temporary relief, don’t be fooled!  When the effect wears off you’ll be back to feeling plugged up and because of how Capsaicin and allyl isothiocyanate work you’ll have worked up even more mucous!