Never Mind the Bullocks, Here's the Science (9 page)

When they woke up the next morning, they realised how dehydrated and delirious they had been. If they hadn’t drunk water until they had urinated, they could have easily died. They might have woken up the next morning still delirious and dehydrated (and not known it). They could easily have ridden and fallen and laughed until they died. Or they might have become even more
dehydrated during the hot night, and not have woken up in the morning.

When I was talking to David up at the Three Ways Roadhouse, at first I couldn’t understand his rule of not going to bed until he urinated. But when I thought about it, I realised that it probably saved his life. David still rides motorbikes. But Ken sold his motorbike after their trip, and took up rowing instead.

References

Almond, Christopher S.D., et al., ‘Hyponatremia among runners in the Boston Marathon’,
New England Journal of Medicine
, 14 April 2005, pp 1550-1556.

Chambers, E.S., et al., ‘Carbohydrate sensing in the human mouth: effects on exercise performance and brain activity’,
Journal of Physiology
, 15 April 2009, pp 1779-1794.

Chatterjee, Asok, et al., ‘Evaluation of a sucrose/electrolyte solution for oral rehydration in acute infantile diarrhoea’,
The Lancet
, 25 June 1977, pp 1333-1335.

Gerlin, Andrea, ‘A simple solution’,
Time
, 8 October 2006, pp 40-46.

Guerrant, Richard L., et al., ‘Cholera, diarrhea, and oral rehydration therapy: triumph and indictment’,
Clinical Infectious Diseases
, 1 August 2003, Vol 37, No 3, pp 398-405.

Guyton, Arthur C. and Hall, John E.,
A Textbook of Human Physiology
, 9th edition, Pennsylvania: W.B. Saunders Company, 1996, pp 43-55, 183-187, 297-313, 833-844, 1059-1070.

Harris, Jason B., et al., ‘Blood group, immunity, and risk of infection with
Vibrio cholerae
in an area of endemicity’,
Infection and Immunity
, November 2005, Vol 73, No 11, pp 7422-7427.

Noakes, Timothy David and Speedy, Dale B., ‘Lobbyists for the sports drink industry: an example of the rise of “contrarianism” in modern scientific debate’,
British Journal of Sports Medicine
, February 2007, Vol 41, Issue 2, pp 107-109.

Place, Nicolas, ‘Go rinse your mouth: a novel way to improve endurance performance?’,
Journal of Physiology
, 1 June 2009, pp 2425-2426.

Sack, David A., et al., ‘Cholera’,
The Lancet
, 17 January 2004, pp 223-233.

Sawka, Michael M., et al., ‘Exercise and fluid replacement’,
Medicine & Science in Sports & Exercise
, February 2007, Vol 39, Issue 2, pp 377-390.

Thapar, Nikhil, et al., ‘Diarrhoea in children: an interface between developing and developed countries’,
The Lancet
, 21 February 2004, pp 641-653.

Wilk, Boguslaw, et al., ‘Effect of drink flavor and NaCl on voluntary drinking and hydration in boys exercising in the heat’,
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Tangled Hair
(A Knotty Problem)

Considering that we humans are basically hairless apes with a big brain, we spend a lot of time worrying about the small amount of hair sitting on the top of our heads. The money spent on hair products is huge. As a result, hair product companies have—from what I have seen in their TV ads—the best laboratories with the most beautiful and/or manly scientists that money can buy.

So, how did these huge hair product companies not notice that you get more tangles in straight hair than in curly hair? Or if they did, why didn’t they tell us?

Hair 101

The hair on our scalp insulates us long-limbed mammals against heat loss, and protects us from the Sun.

Each individual hair can support an 80 g weight. So if you could weave all of your 100,000-150,000 scalp hairs into a single rope, it could hold up an 8-12 tonne truck.

Each individual hair is a long, thin fibre made of keratin. Keratin is the tough and insoluble protein found in hair, wool, fur, skin, silk, horns, fingernails, porcupine quills, and hoofs—and even some hair shampoos. There are different types of keratin—some hard, some soft.

First, a bunch of smaller amino acids (mostly glycine and alanine) join together to make each individual keratin protein. The shape of the keratin protein is like a helix, or spiral staircase. Four of these helices twist around each other to make a protofibril. In turn, eleven protofibrils are bundled together to make a microfibril, which in turn are bundled together to make a macrofibril, which in turn are bundled together to make a hair shaft.

Each individual hair shaft is made by a single hair follicle. You have about 100,000-150,000 hair follicles on your scalp when you are born—and that’s all you will ever have. Thanks to the nerves that surround each of these follicles, you know when your hair brushes against something.

The hair follicle is special—it’s one of the very few organs in an adult that regenerates in a cyclical fashion.

Colour of Hair

The colour of hair usually comes from a pigment called melanin. (Once again, as is always the case with the human body, everything is more complicated than first thought. There are actually different types of melanin: eumelanin is the most common and gives the shades from brown to black, and pheomelanin gives the yellow-blond and red colours.)

Black hair contains lots of melanin, while light brown and blond hair contains less. And the hair of people with albinism contains no melanin at all.

But red hair is special. Not only does it contain melanin, it also contains some iron. So ‘rusty’ is actually a scientifically correct nickname for someone with red hair.

Shaft’s the Name

Cutaway of the microscopic structure of a human hair shaft.

And, a diagram of a hair follicle.

Baldness

About 40% of men go bald.

In males, baldness is programmed by the male sex hormone, testosterone. The testosterone gets converted into dihydrotestosterone (DHT). In youth, DHT puts hair on males. But in later years (and we don’t know why), DHT has the completely opposite effect. It seems to shut down the follicles that have lots of DHT receptors. In fact, some men with very high levels of testosterone go bald at an early age. (Surprisingly, not only do some follicles have the receptors for DHT, they carry the enzyme that converts testosterone to DHT. This makes them ‘Suicide Follicles’, carrying the means of their own loss of function.)

A hair follicle has only a limited number of cycles of growth and rest before it stops working – probably around 25 or so. (Once again, we don’t know why.) The hair product company L’Oréal studied ten men over a 14-year period in the 1980s and 1990s. They shaved off the 200-300 hairs in just one single square centimetre on each man’s head, and counted how many of the hairs grew back, and how quickly they did so. They found that men who tended to go bald early had hair follicles with very short cycles of growth and rest. It seems to be a case of Live Fast and Die Young for some cases of baldness.

Getting back to testosterone, if a male is castrated at a very early age (i.e. before puberty), he never makes any large amounts of testosterone. So the castrated male, a eunuch, will never go bald.

Hair 102

Each hair follicle manufactures its hair shaft from the base (unlike plants, which do most of their growing at the tip). Hair follicles have a long growing period, followed by a short resting period.

The follicle grows hair for up to five years in women, but only three years in men. In that time, a single hair can grow 75 cm in a woman, but only 45 cm in a man (roughly 10-15 mm per month). This is why women can grow their hair longer than men can.

After the growing period comes to an end, the follicle takes a rest for about three months and shrivels up. The root of the hair is now very shallow, only about half a millimetre below the surface. At that stage, the hair shaft can be easily pulled out by a comb, or a strong wind, or by rubbing against something. At any given time, about 10% of the hair follicles are resting.

The hair follicle then wakes up and starts growing a new hair. This new hair pushes out any old hair still stuck in the follicle.

We still don’t know the working of the mechanism that stops these cycles from being synchronised in the hair follicles. But it’s good that they are not synchronised. If they were, all of our hair would fall out at the same time, instead of at the steady rate of 50-100 hairs each day.

Hair Tangles—A Knotty Problem

It was a French physicist who first took this new look at hair.

He needed a problem for his students. In fact, this preliminary study of his was originally aimed at high school students, to get them interested in science. This is why it’s more a preliminary study, rather than a fully developed work.

He started thinking about scalp hair, which is a collection of about 100,000 individual shafts. He thought that perhaps it might be possible to model this complex system of 100,000 separate units in a simple way.

Even today, there is still no single widely accepted model that predicts how hair will behave. And there is so much that we still do not know about ‘tangles’—e.g. how they form, how they resolve, why they form here rather than there, and why there are sometimes so few or so many.

Hair Tangles—Theory

He developed a theory of geometric modelling of hair, setting up a simple model based on the science of polymer dynamics.

He made a few assumptions. First, he modelled straight hair (or a bunch of straight hairs) as a rigid segment with a known length. Curly hair was modelled as having a straight section and a wavy section. Second, he assumed that these hair strands are fixed into the scalp at one end but point in all possible directions at the other end. A hair can also change from pointing in one direction to pointing in any other direction. And, third, he assumed that any two hairs, or any two groups of hairs, can cross each other, and they can do so at a variety of angles.

There were other assumptions as well. The hairs are also subject to random turbulence. They can move independently of each other. But occasionally they can also move in a coordinated motion—as in the ads on TV, when the female model’s metre-long hair falls like a slow-motion wave.

The hair product industry has its special language to describe hair—but so does science. ‘Oily’ made the physicist think of ‘cluster formation and binding energy’, while ‘straight and curly’ started him ruminating on ‘general geometry and spatial organisation’. ‘Thin and thick’ was more than just a description of diameter—to a physicist, it was ‘the influence of elementary characteristic properties on general behaviour’.

His theory predicted that straight hair should have more tangles than curly hair. This is the opposite of what you would expect.

Bad Hair Day