Where does this come from, and can I check it?

Tough structural proteins form non-living outer protective structures. The figure is taken from Encyclopaedia Britannica, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.

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Yes. It sits on the Human Body shelf, one of 1,090 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.

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Mondo Knows Facts

Hair and fingernails are composed of the protein keratin

Tough structural proteins form non-living outer protective structures

Both hair strands and fingernails consist primarily of keratin, a tough fibrous protein also found in outer skin layers. The visible parts of hair and nails are made of non-living dead cells packed with keratin, which explains why cutting them causes no physical pain.

Where this comes from

Encyclopaedia Britannica

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Fingernails grow almost four times faster than toenailsGreater blood supply and physical use stimulate faster nail plate growth Human scalp hair grows at about one centimetre per monthHair follicles cycle through growth rest and shedding phases continuously Hair shampoos are formulated slightly acidic to match scalp chemistrySlightly acidic wash formulas protect the scalp's natural protective barrier Melanin determines skin hair and eye colourationSpecialised melanocyte cells produce pigments that absorb ultraviolet radiation The human body contains up to four million sweat glandsEccrine and apocrine glands secrete watery sweat to cool body surface The human retina contains over one hundred million light receptorsRods enable dark peripheral vision while cones register fine detail and colour

Tags: keratin, hair, nails

Hair and fingernails are composed of the protein keratin: the short answers

Where does this come from, and can I check it?: Tough structural proteins form non-living outer protective structures. The figure is taken from Encyclopaedia Britannica, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
Is this really a human body fact?: Yes. It sits on the Human Body shelf, one of 1,090 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
What else can I read about it?: The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.