Questions on everyone’s lips
WHY DOES THE HAIR ON OUR HEAD KEEP GROWING?
EVER wondered why we get wrinkles or why our nose runs in the cold? How about why the hair on our head keeps growing but the hair on our arm does not?
Our bodies do some mysterious things. Let’s look at the answers behind some of them.
WHY DO WE GET WRINKLES?
Kids mostly have smooth, tight skin. As adults get older, their skin is a little looser and more likely to have creases or wrinkles. Wrinkles are a normal part of ageing.
Young, healthy skin has a smooth outer layer called an epidermis that acts as a barrier to stop water and other things from entering your body.
The dermis — the middle layer of skin — has natural substances called collagen (a protein that keeps skin firm) and elastin (fibres that gives skin its stretchiness).
Adults’ bodies make about 1 per cent less collagen in their skin each year, so that as we get older, skin gradually gets thinner, more fragile and less firm.
Our environment also makes our skin age: sun and pollution can change your skin’s colour, make it spotty or freckly, dry it out and reduce the amount of collagen and elastin your body makes. The amount of fat in the innermost layer — called the subcutaneous layer — decreases as we get older, too, so older skin doesn’t look as plump.
WHY DO WE GO WRINKLY IN THE BATH?
In the past few years, some scientists have been testing out hypotheses to possibly explain what some of us call prune fingers and toes.
Experiments around 2011-12 found that people with wrinkly fingers could more easily pick up marbles. This supported the idea that prune fingers and toes are like the tread on your sports shoes or on the tyres of a bike or car, to stop us slipping on wet surfaces.
But when other scientists tried to repeat these experiments in 2014, they found that having wrinkly fingers made no difference to how well someone could grip an object.
WHY DOES OUR NOSE RUN WHEN WE’RE COLD?
Cold, dry air irritates the lining of our nose, causing the nasal glands to produce more mucus to keep the lining moist. This can mean a runny nose and drips from our nostrils.
It’s also the job of the nose to warm the air we breathe in so it doesn’t irritate the lungs.
The cold, dry air also stimulates nerves inside the nose, which then send a message to the brain to increase blood flow to the nose. The increased blood flow to blood vessels in the nose warms the air passing over them.
We all make about 1.4 litres of mucus, also known as snot, every day, whether we’re sick or healthy. And we swallow most of it. Yuck.
Most of the time, we don’t notice that we’re making and swallowing it, but when we’re suffering from an allergy, a cold or the flu, there seems to be so much snot we can feel like we’re drowning in it.
We’re not. We don’t produce any more snot when we’re sick than we do when we’re healthy. It just changes to become thicker or runnier and those changes are noticeable and make us feel uncomfortable.
Good mucus management
Colds and other viruses such as the flu and coronavirus are contagious and spread by droplets of snot or spit (called saliva). You can do a lot to keep yourself and others healthy by:
Keeping your hands out of your mouth
WHY DOES THE HAIR ON OUR HEAD KEEP GROWING?
Each head or body hair grows out of a little pocket in your skin called a follicle. Tiny blood vessels in your skin bring a constant supply of nutrients to the root of each hair at the bottom of the follicle.
With the nutrients, the hair builds news cells, which pushes the older cells out of a hole in the follicle, which is your hair growing.
It’s a bit like building a tower of wooden blocks or Lego but making it taller and taller by adding more blocks or bricks from the bottom.
Your body makes head hair and body hair the same way.
Each hair follicle on your head grows its one hair for perhaps two to six years (the active phase) and then it takes a break (the dormant phase).
Because you have about 100,000 hair follicles on your head, you don’t notice when a few follicles take a break because there are plenty of other follicles on duty.
The difference between body hair and head hair is in the length of the active phase.
Each body hair follicle is only in an active phase for about a month, which means each body hair only gets to grow a few millimetres before the hair follicle goes off duty and soon falls out.
So it’s clear HOW our head hair keeps growing, but WHY is a tricky question to answer.
There’s an idea that perhaps when our ancestor Homo erectus evolved to stand up straight and march out of the forests (where other primates stayed) into the open grasslands, we needed thinner body hair to help us stay cool, but longer, glorious head hair as shade for our fantastically big, clever brains.
Another idea is that we evolved to become less obviously furry because those early ancestors who could show off fit, healthy, parasite-free bodies were more likely to find a mate.