Tech UPTechnologyCurious things about hair and shampoo

Curious things about hair and shampoo

The hair, that dark object of desire. Women are concerned about having it beautiful and men that it does not fall out, something on the other hand inevitable: as a teacher said, the only thing that stops hair loss is the ground and to preserve it, a little box.

The number of hairs we have on our heads depends on their colour: redheads have around 170,000 and brunettes 200,000, while blondes fall somewhere in between. Hair is made up of cells that sprout in the form of a strip from tiny holes on the head. Its life cycle is curious. For three years it grows, after which it dies in about 3 weeks. But it doesn’t fall out right away, it stays in the scalp for at least 3 more months , until the new hair pushes it out and falls out. In order for them to slide gracefully out of these holes, there are bags on the skin that secrete a lipid that serves as a lubricant: it is what we commonly call fat. If it weren’t for these sebaceous glands, we would feel very itchy.

This is how hair gets dirty

As it grows, this liquid fat solidifies, forming scales that cling to the scalp and make it stiffer, which is why when we run our fingers through our hair we notice it is stiff and greasy. In addition, those little packets of fat are like magnets for different elements that float in the air: dust and dirt, fragments of microscopic insects, odoriferous molecules – apparently, nitrogen molecules from cut onions have a special predilection for binding to fat hair, as well as traces of cigarette smoke, soot, pollen… In this way, each hair on our head behaves like one of those sticky flytraps : in the event that the hair measures 23 cm and has about 90,000 , means that there is a little more than 20 kilometers of dirt catcher on the head, which in two days will have about 15 grams of dirt stuck to it. If he did not wash his hair for a whole year , the level of dirt would reach 3 kilos and in ten years he would have accumulated the weight equivalent to a human being.

That is why it is so important to wash your head. If we look closely, shampoo ads promise us cleanliness and beauty for our hair while showing us hair wrapped in foam. However, the foam does not clean . Manufacturers include it because very few of us would buy a shampoo that didn’t foam. In reality, cleaning is carried out by the detergent it contains, which is 15% of the content of the shampoo bottle. Their job is very simple: remove the plates of grease and dirt stuck to the hair.

Conditioners and electrical charge of the hair

Now, the situation is not as simple as it may seem. The hair is electrically neutral but the shampoo only acts on the areas where there are positive charges , so the hair loses its electrical balance. The hair, electrified by the action of the shampoo, tend to repel each other, forcing them to perform a curious dance, as if it were a twist. If we brush our hair just after drying it, what we get is to aggravate the situation, because if we brush 100 times the electrical charge of the hair also increases almost 100 times.

The only solution to avoid this mess is to put the head in a basin of lard . Thus, pork fat – or duck fat if we are more chic – mimics our own fat, keeping the different electrical surfaces that occupy contiguous places isolated. Since that would not be very pleasant, we have no choice but to use the softener and the fixative. The softener provides the positive electrical charges necessary to balance the negative ones that the shampoo does not act on, and the fixative is nothing more than a liquid plastic whose only function is to leave the hair where it has been during brushing. In other words, keep the hairstyle we want.


Bodanis, D. (1988) The secrets of a house, Salvat

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