Why Do Fingers Wrinkle? 6 Body Quirks Explained
Many of the body's reactions seem random, but nearly all of them have a specific explanation. Here we look at six of them, from fingers that wrinkle in water to the extra bones a baby has.
Why fingers wrinkle in water
For a long time, it was assumed that the skin swelled up like a sponge. That is not the case. The wrinkling is controlled by a nerve.
In 1936, two British doctors observed that in patients with a severed nerve in the hand, the affected fingers did not wrinkle. Water gets into every finger equally. What makes the difference is the nerve.
After a few minutes of soaking, the nerve signals the blood vessels under the fingertip to narrow. The skin loses volume and folds, like a sheet when the mattress is pulled out from under it. Some neurologists use this reaction to check whether a nerve is working.
Its most likely purpose is to improve grip. In 2013, at Newcastle University, volunteers with wrinkled fingers moved wet marbles faster. The grooves would channel water away, like the tread on a tyre. However, other teams have not been able to replicate this. It is the best hypothesis, not a closed case.
Why we sneeze in sunlight
Sneezing when coming out of a tunnel or looking at the sun happens to between one in five and one in three people. Aristotle was already wondering why. In the 17th century, Francis Bacon faced the sun with his eyes closed, did not sneeze, and concluded that the cause lay in the eyes. In English it is known as the ACHOO reflex, after a medical acronym.
The most widely accepted explanation is crossed signals. The optic nerve runs very close to the trigeminal nerve, which detects itching in the nose. A sudden burst of light overloads the neighbouring nerve, and the brain interprets it as something being in the nose.
It is also inherited as a dominant trait. If either parent has it, the chance of inheriting it is around one in two.
Why you see stars when you stand up too fast
When you stand up, gravity shifts between half a litre and a litre of blood towards the legs. Pressure sensors in the neck and the aorta detect this and speed up the heart. But they need a few seconds.
During that interval, less blood reaches the head. Vision is the first thing to suffer: sparks, black spots or tunnel vision appear. It is similar to what happens in a shower when someone flushes the toilet: the pressure drops and then recovers.
Why your leg falls asleep and then tingles
When you keep your legs crossed for a long time, it is not just the nerve that gets compressed. The vessels that supply it are compressed too. Without oxygen, the thickest fibres, those responsible for touch and position, are the first to stop working. That is why the leg feels as if it belongs to someone else.
When the pressure is released, blood returns and the nerves start up again in a disorderly way, firing signals uncontrollably. That is the tingling. It does not mean the leg is being damaged; it means it is recovering.
What hiccups are and what causes them
The diaphragm contracts abruptly and pulls in a sudden rush of air. A fraction of a second later, the glottis snaps shut. That closure produces the hiccup sound. Hiccups are triggered by eating quickly, fizzy drinks or having a very full stomach.
One hypothesis links them to tadpoles, which pump water across their gills with an almost identical movement. Another connects them to breastfeeding: hiccups would help babies expel the air they swallow while feeding. In 2019, at University College London, researchers observed that each hiccup in a newborn activates the brain in a way that could teach the baby to control its breathing.
The most extreme case is that of Charles Osborne, an Iowa farmer who had hiccups from 1922 to 1990.
Why a baby has more bones than an adult
A figure of 300 bones in a baby circulates online. Textbooks usually say around 270. The number varies because many parts are still cartilage. An adult has 206.
The missing bones do not disappear: they fuse together. The skull starts out divided into plates that overlap so the head can pass through the birth canal. Each half of the hip begins as three bones and ends up as one. The sacrum is made up of five fused vertebrae.
This process goes on for about 25 years. The last area to close is the end of the collarbone that meets the breastbone, which may not fuse until after age 25. That is why some forensic experts examine it on a scan to estimate whether a person is over 21. On many X-rays, the joins can still be seen.
Frequently asked questions
Why do fingers wrinkle in water?
Because a nerve signals the blood vessels under the fingertip to narrow, so the skin loses volume and folds. It is not simply because the skin absorbs water.
Why do some people sneeze when they look at the sun?
The most widely accepted explanation is that the optic nerve runs very close to the trigeminal nerve, and a burst of light makes the brain interpret that something is in the nose. It is a dominant inherited trait.
Why do you see black spots when you stand up quickly?
When you stand up, blood moves down towards the legs and the heart takes a few seconds to compensate. During that time less blood reaches the head and vision suffers.
How many bones does a baby have?
Textbooks usually say around 270, compared with 206 in an adult. The bones are not lost: they fuse together as the body grows.
Informative article written with the help of AI tools from the verified script of the video. The video is in Spanish.