The Effect seen in most Superficial Epidermal Layers
A hypothetical drug causes blood vessels to grow from the dermis into the superficial stratum granulosum of the epidermis it will thicken the epidermal layers. Epidermis is the outermost of the three layers that make up the skin so a hypothetical drug will thicken such an outermost layer.
The melanocytes are accountable for skin color that is observed in the basal cells. The epidermis has no blood stocks and depends on the spread from the dermal cells for its metabolic demands. The dead-cell zone of the stratum corneum presents the stability from H2O failure that allows vertebrates to remain on the area.