Agar-agar (seaweed extract) is a polysaccharide that comes from several varieties of red algae. Agar is used in making ice creams, jellies, icings, preserves, and for thickening milk and cream. It can be used as a substitute for gelatin.
Agar, in rare situations, can be a mild allergen and acts as a laxative. It is on the GRAS list.