  Purpose. This study investigates in silico the contribution of the hair
follicle to the overall dermal permeability of small molecules, as published
experimental work provides inconclusive information on whether the follicular
route favours the permeation of hydrophobic or hydrophilic permeants. Method. A
study is conducted varying physico-chemical parameters of permeants such as
lipophilicity, molecular weight and protein binding. The simulated data is
compared to published experimental data to discuss how those properties can
modulate the contribution of the hair follicle to the overall dermal
permeation. Results. The results indicate that the contribution of the
follicular route to dermal permeation can range from negligible to notable
depending on the combination of lipophilic/hydrophilic properties of the
substance filling the follicular route and the permeant. Conclusion.
Characterisation of the substance filling the follicular route is required for
analysing the experimental data of dermal permeation of small molecules, as
changes between in vivo and in vitro due to handling of samples and cessation
of vital functions can modify the contribution of the follicular route to
overall dermal permeation, hence hindering data interpretation.
