Distribution of prehaptens, prohaptens and pre/prohaptens across the GHS 1A and 1B categories of skin sensitizers. There are 87 LLNA sensitizers (35 1A [strong] and 52 1B [weak]) and 57 human sensitizers (26 1A sensitizers and 31 1B). GHS, United Nations Globally Harmonized System of Classification and Labeling; LLNA, murine local lymph node assay; Pre, prehapten; Pre/Pro, pre- and/or prohapten; Pro, prohapten; U = unknown.