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Chitin is one of the main components in the cell walls of fungi, the exoskeletons of insects and other arthropods (such as crustaceans) as well as fish and frogs. It is a polysaccharide that is constructed from units of acetylglucosamine (more completely, N-acetyl-D-glucose-2-amine). These are linked together in beta-1,4 fashion (in a similar manner to the glucose units which form cellulose). In effect, chitin may be described as cellulose with one hydroxyl group on each monomer replaced by an acetylamine group. This allows for increased hydrogen bonding between adjacent polymers, giving the polymer increased strength. Chitin is the second most abundant polysaccharide in the world (after cellulose). Chitinases break down chitin and are a part of the defence mechanism of mammals against chitin-containing parasites in lower life forms. Under certain circumstances, chitin can act as an allergen. Research using murine models has shown that chitin is a size-dependent microbial-associated molecular pattern (MAMP) that can induce an immunological response via pattern recognition receptors. Medium-sized chitin micro-particles (CMPs) have been shown to induce inflammation, while small-sized CMPs reduce inflammation. Additionally, mammalian chitinases may play a key role in mediating the T-helper 2 cell-driven inflammatory response that is commonly associated with asthma. The high prevalence of asthma among people working with chitinous substances, such as crabs and fungi, suggests that chitin might be an allergen playing a significant role in the development of asthma.

Tri-N-acetylchitotriose is an oligosaccharide that may prevent the action of certain prolamins (antinutritional peptides) from some cereals (e. g. wheat, barley, and rye) that adversely affect in vivo the intestinal mucosa of coeliac patients. (PMID: 10399351).

A branched amino trisaccharide comprising an N -acetyl-alpha-D-galactosamine residue at the reducing end, to which are (1->3)- and (1->6)-linked two N -acetyl-alpha-D-glucosamine residues." []

A branched amino trisaccharide comprised of two N-acetyl-beta-D-glucosamine residues linked (1->4) and (1->6) to N-acetyl-alpha-D-galactosamine." []

A linear amino trisaccharide consisting of three N-acetyl-beta-D-galactosamine residues linked (1->4)." []