Hair is obviously protein, so why can’t the stomach handle it?

Since when, hair has become one of the most important items in self-image management for us young people in the new era. We have been committed to growing thick and beautiful hair, going further and further on the road of "how to prevent baldness", but ignoring the deepest essence of hair - it is protein.

Some people may be curious, as hair is a protein, why can't it be eaten (the stomach can't digest it)? Cats lick their fur every day, and it goes into their stomachs, so how can their fur be eaten? Sometimes, when they vomit up small balls of hair, is it because the stomach can't digest the hair, or is it because there is too much hair and the stomach can't digest it all and has to vomit it out?

Don’t be impatient, we’ll talk about it slowly.

Hair from macro to micro

Let's first introduce human hair from a macroscopic perspective. Hair, as the name implies, refers to the hair growing on the head. In addition to adding beauty, hair is mainly used to protect the head. Fine, soft and fluffy hair is elastic, can withstand minor collisions, and can also help the evaporation of sweat on the head. Among all the hair on the human body, hair can grow the longest and grows the fastest.

Hair has no sense of pain or touch. It is not a human organ and does not contain nerves or blood vessels. The pain felt when pulling hair is due to stimulating the tactile nerves on the scalp.

Hair in biology is a general term. In addition to the hair shaft exposed on the epidermis, it also includes the hair follicles below the epidermis of the scalp. At the bottom of the hair follicle, epidermal cells continue to divide and differentiate, growing hair shafts. Sebaceous glands secrete sebum, providing natural protection for hair.

Each hair is composed of the epidermal scale layer, cortex layer, and medulla layer. The epidermal scale layer is the outermost layer of the hair, which is usually translucent or colorless, so it allows the natural hair color to show through; the cortex layer accounts for 80% of the hair, where natural pigments are deposited, and the natural hair color is due to it; the medulla layer is located in the center.

Hair is a fiber with a complex structure. Alpha-keratin is the main component of hair fibers. Other components include lipids, water, pigments and trace elements. Speaking of this, there is another issue that still troubles the French. It is worth mentioning that the arsenic content in Napoleon's hair exceeds the normal value. So far, it has not been determined whether Napoleon died of poisoning or stomach cancer.

It is worth pointing out here that the hair of all vertebrates is composed of α-keratin, and cats' hair is no exception.

The secret of why hair cannot be eaten lies in this magical keratin. And the so-called "eating hair" by cats is not what we imagine.

Microscopic process of protein digestion

Before talking about keratin, let's briefly review the process of protein digestion and absorption by the human body. We all know that protein, as a large molecule, is not easily absorbed without digestion. Generally, food protein can only be absorbed after being hydrolyzed into amino acids and small peptides. Since saliva does not contain enzymes that hydrolyze protein, the digestion of food protein starts in the stomach and ends in the small intestine. During this period, under the action of gastric acid, pepsin, trypsin and intestinal protease, protein macromolecules are broken down into small peptides and even amino acids, and finally absorbed by the small intestinal mucosal cells. The above is the main way of protein digestion and absorption in the traditional sense. With the deepening of scientific research, scholars have discovered more "special carrier transport channels" for small intestinal mucosal cells to directly absorb peptides. Humans have a deeper understanding of protein absorption, which will not be mentioned here for the time being.

The Secret of Keratin

As we have introduced above, the way the human body digests and absorbs protein, we know that if protein wants to be digested by the human body, its molecular structure must first be destroyed and then broken down into small peptides or amino acids.

「From top to bottom」 Intermediate filament protofibril Primary fibril Double-stranded helix One helix

α-keratin is the main protein that makes up hair and is one of the fiber structural protein family. Because it contains more cysteine, the content of disulfide bonds that play a cross-linking role in the protein peptide chain is particularly high. Therefore, the chemical properties of keratin are particularly stable and it is extremely difficult to dissolve and digest in the human body environment.

This is why hair cannot be eaten, because keratin is difficult to break down under normal circumstances.

Cats also cannot digest the hair that they lick into their stomachs. Cat owners know that cats need to eat cat grass or hairball remover regularly to help expel the accumulated hair in their bodies. Although it is called hairball remover, it does not have the effect of removing hair. The main ingredient of most hairball removers is oil. Some cats will vomit and spit out hairballs after eating hairball remover, mostly because the stomach is irritated by oil.

It is worth mentioning that although the hair of all vertebrates is composed of α-keratin, some scholars have conducted keratin comparison tests on the hair of any different animals and human hair, and found that there are still significant differences in the components of the two, which is reflected in the content of high-sulfur protein.

Although hair cannot be eaten, scientists have continuously researched and explored animal feathers and have developed a variety of processing methods. After high temperature, high pressure, acid, alkali or enzyme treatment, keratin can be decomposed into short peptides or free amino acids for livestock and poultry to eat. Feathers have now become a recognized potential high-quality protein source with high nutritional value and stable quality for use in the feed and food industries. They are also shining in many fields such as environmental protection, fertilizers, and pharmaceuticals. Scientists have never stopped exploring the treasure of keratin, and there must be more surprises waiting for scientists to discover!