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In a story I'm working on, there are some creatures that eat hair, wool, fur, and anything similar.

They're not mites or insects, but are (very roughly) the size of humans.

Is there any realistic reason that a creature would need to eat hair?

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  • $\begingroup$ Are they eating their own hair? If so, it's a disorder called trichophagia (specific to eating hair). $\endgroup$
    – Vincent
    Apr 22, 2015 at 3:12
  • $\begingroup$ @Vincent, no, not their own hair. $\endgroup$
    – Joe
    Apr 22, 2015 at 4:10
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    $\begingroup$ As a source of dietary fiber? You may or may not have noticed that dogs & cats (and probably other animals) wind up consuming hair as part of the grooming process. Perhaps they then evolve an enzyme that breaks the hair down, allowing the nutrients to be re-used. From there it's a short step to becoming a specialized capilovore. $\endgroup$
    – jamesqf
    Apr 22, 2015 at 5:07
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    $\begingroup$ Ask yourself: Why is hair made from keratin, which is indigestible to almost everything? (Hint: I just told you the answer.) Then ask yourself: Does the hair in my story NEED to be as indigestible as keratin? $\endgroup$
    – dmm
    Apr 22, 2015 at 14:26
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    $\begingroup$ I'd just like to point this out: drmcninja.com/archives/comic/10p14 $\endgroup$
    – thanby
    Apr 22, 2015 at 16:15

6 Answers 6

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The creature evolved from a carnivore (or omnivore) and it's ancestor was a messy eater. Food was scarce, too, so they developed to be able to make use of the hair they digested.

Over time, The ability to produce Keratin on their own has disappearead (which should be biologically feasible since with the keratin from their prey this would not be a disadvantage), so now, to have their hair, nails or claws, maybe scales, grow, they depend on an external keratin source.

It might even be that the amount of keratin they digested determined the amount / strength / texture of their own hair, thus influencing their attractivity to the other sex.

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    $\begingroup$ The problem with this idea is that, in practice, proteins (like keratin) have to be broken down into individual amino acids before they can be absorbed. Thus, even if the creature evolved a way to digest keratin, they wouldn't absorb it as keratin, but as just a bunch of amino acids. Thus, they'd still have to resynthesize any keratin they needed themselves. $\endgroup$
    – Ilmari Karonen
    Apr 22, 2015 at 15:24
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    $\begingroup$ Thank you for that insight, @IlmariKaronen. Would it still be possible that the creature benefits from digesting them, maybe if it was easier to resynthesize the keratin from those amino acids than from other food sources? $\endgroup$
    – Burki
    Apr 22, 2015 at 15:38
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    $\begingroup$ Maybe. Keratin is quite rich in cysteine, a semi-essential sulfur-containing amino acid that gives keratin its toughness by forming disulfide cross links between the protein chains. So, yeah, if you needed a lot of cysteine for something (e.g. to make more keratin), digesting keratin would be a good way to get it (if you can do it, that is; keratin is notably hard to digest, although simple mechanical grinding apparently helps quite a bit). $\endgroup$
    – Ilmari Karonen
    Apr 22, 2015 at 16:10
  • $\begingroup$ According to a citation-less line in the keratin wiki certain species of fungi feed on keratin. Perhaps their gut flora need it? $\endgroup$
    – Jake
    Apr 22, 2015 at 17:40
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    $\begingroup$ @Jake I followed that link thinking it was to a wiki all about keratin -- now that would be something... $\endgroup$
    – k_g
    Apr 23, 2015 at 0:57
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These creatures evolved in a symbiotic relationship with a larger creature with fast growing hair. If the Fuzzie's hair was allowed to grow unchecked, the poor things would soon become unable to move, but they need lots of hair because the climate is very cold. Our Eaters would groom/consume the creatures hair as they slept, and in exchange were allowed to live in the Fuzzie's cozy burrows.

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Well this is a very scientific and tough explaination. But stay with me: Assuming they are human-like if they grind the hair very well with their teeth they would get a dust with a quite large surface. The dust contains mostly keratine which - in combination with a strong acid (as in a stomache) forms tyrosine and decarboxylase. The large surface helps speeding up the process enough so it hasn't passed the whole digestive tract before everything is done. Tyrosine combined with the enzyme tyrosine 3-monooxygenase (which is formed in the brain or - more relevant in the adrenal glands and also found in the stomache) becomes L-3,4-dihydroxyphenylalanine which in combination with the formerly mentioned decarboxylase becomes dopamine. Well-grinded in the beginning it should be possible to speed the whole process up enough to create dopamine early enough to absorb it in the colon. Within a reasonable amount of time it will travel to the brain. SO what's the point? Well, several neurological conditions, most famously including Parkinson's disease have shown to result from a lack of dopamine-secreting neurons in the midbrain area called the substantia nigra. Eating hair would not cure Parkinson's disease or other neurological conditions, but it would help supress the syndroms. And it makes happy (Yes, raising the dopamine-levels in your body would get you stoned).

So why don't people do it? You can easily have the body create more dopamine by injecting adrenaline or taking amphetamines or many other ways. So people get stoned on dopamine, but use less discusting ways then eating hair.

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    $\begingroup$ So, to make this long story short, the creature is on drugs ? $\endgroup$
    – Jorge Aldo
    Apr 22, 2015 at 19:04
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Far, far in the future, many animals have developed a mechanism against predators. There are deadly toxins in their bodies, flowing around in vein-like structures. Their hair, however, is like present day hair, made of keratin. The only part of an animal that one could safely eat would be the hair. Such an animal would also have to eat plants, so that it gets enough nutrients and calories.

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Use the hair of the animal/person as an important digestive additive and set them as a predatory carnivore.

Large predatory cats are healthier when they eat the hair of the animal that capture. This could be used by your carnivore to ensure a healthy diet (and prevent watery poop). There was a study done to prove the digestive benefits of the "roughage" from fur, and the results came back that even when given beef with added nutrients and vitamins, the cats who ate the animals with the hair ended up healthier overall.

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This wouldn't be as a source of nutrition, but the hair could be routed outside of traditional digestion and into some kind of storage, and the creature could projectile-vomit hairballs as a defence mechanism.

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