An increased ability of a chemical to hydrogen bond can result
in a slower diffusion of it through skin. The pyrethroids do not have
ionizable moieties that could participate in hydrogen bonding, but
have some functional groups (e.g., carboxyl) that are available for this
type of bonding. The differences in structure between bifenthrin,
deltamethrin and cis-permethrin are the halogens (Cl for permethrin,
Br for deltamethrin, Cl and F for bifenthrin), a cyano group in
deltamethrin, and a different aromatic group for bifenthrin.