Science, Tech, Math › Science What Is Keratin and What Is Its Purpose? Share Flipboard Email Print SUSUMU NISHINAGA / Getty Images Science Chemistry Biochemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated August 29, 2018 Keratin is a fibrous structural protein found in animal cells and used to form specialized tissues. Specifically, the proteins are only produced by chordates (vertebrates, Amphioxus, and urochordates), which includes mammals, birds, fish, reptiles, and amphibians. The tough protein protects epithelial cells and strengthens certain organs. The only other biological material possessing similar toughness is the protein chitin, found in invertebrates (e.g., crabs, cockroaches). There are different forms of keratin, such as α-keratins and harder β-keratins. Keratins are considered examples of scleroproteins or albuminoids. The protein is rich in sulfur and insoluble in water. The high sulfur content is attributed to the richness of the amino acid cysteine. Disulfide bridges add strength to the protein and contribute to insolubility. Keratin is not typically digested in the gastrointestinal tract. Keratin Word Origin The word "keratin" comes from the Greek word "keras" which means "horn". Examples of Keratin Bundles of keratin monomers form what are called intermediate filaments. Keratin filaments may be found in the cornified layer of the skin's epidermis in cells called keratinocytes. The α-keratins include: hairwoolnailshoovesclawshorns Examples of β-keratins include: scales of reptilesreptile nailsbird clawstortoise shellsfeathersporcupine quillsbird beaks The baleen plates of whales also consist of keratin. Silk and Keratin Some scientists classify the silk fibroins that are produced by spiders and insects as keratins, although there are differences between the phylogeny of the materials, even if their molecular structure is comparable. Keratin and Disease While animal digestive systems aren't equipped to deal with keratin, certain infectious fungi feed on the protein. Examples include the ringworm and athlete's foot fungus. Mutations in the keratin gene can produce diseases, including epidermolytic hyperkeratosis and keratosis pharyngis. Because keratin is not dissolved by digestive acids, ingesting it causes problems in people who eat hair (tricophagia) and results in vomiting of hairballs in cats, once enough hair has accumulated from grooming. Unlike felines, humans don't vomit hairballs, so a large accumulation of hair in the human digestive tract can cause the rare but fatal intestinal blockage called Rapunzel syndrome.