Are Chitosan and Chitin the same thing?

No, they’re not. Chitin is an element in the composition of the shells of crabs and shrimp. It is an animal-derived dietary fiber polymer whose molecular weight exceeds one million and doesn’t melt in water or in acid. Chitosan is derived from Chitin by deacetylation. Chitosan also comprises polymers whose molecular weight is several hundred thousand. Chitosan does melt in weak acids but doesn’t melt in water.