Hypodermis offered a resistance to the drug permeation
and significantly slowed down the release rates by a 1.3 factor
for every vehicle. This was an obvious effect of the presence
of hypodermis as a supplementary barrier in
permeation experiments. More interestingly, the hypodermis
lipophilic barrier retained the caffeine inside the top
hydrophilic layers of the skin, namely the dermis and epidermis.
The presence of the hypodermis had an influence
upstream of the diffusion flux.