Carrageenan is a family of naturally-occurring high molecular weight polysaccharides extracted from red seaweed. The main seaweed types include Eucheuma, Chondrus and Gigartina which yields kappa, iota and lambda carrageenan.

The carrageenan structure is made up of repeating galactose and 3,6 anhydrogalactose units, both sulfated and non-sulfated joined by alternating alpha 1-3 and beta 1-4 glycosidic linkages.
The kappa, iota and lambda carrageenans differ in properties mainly due to the number and position of ester sulphate groups on the galactose units. While kappa forms a brittle gel, iota forms an elastic gel and lambda does not form a gel. Based on their properties, they find use as stabilizers, thickeners, suspending agents, gelling agents and flow regulators in pharmaceutical dosage forms.