The first sequences of keratins revealed that keratins could be grouped into two categories based on their sequence homologies. These two groups of keratins were named as type I and type II keratins. These two categories also represent the first two categories of the superfamily of intermediate filament proteins.
Keratins in this table are classified in the first two columns according to the nomenclature established in 2006. Other names previously used are listed in columns 3 and 4.