The dermis contains a complex vascular system arranged in three plexuses. Many structures are supplied retrogradely or have their own vascular and nervous plexuses, e.g., the hair follicles. The varying morphology of pathologic changes is due to certain pathologic processes being principally associated with a particular stage of the vascular system and consequently taking place largely in a particular layer of the skin.

Skin blood vessels are difficult to distinguish in histological sections. The major veins have special wall structures in various skin regions to meet the particular physiological requirements of say the arm or leg. Contraction of the venous wall may cause the tunica muscularis to appear thick so that the vessel looks like an artery to the inexperinced eye. In addition, the venous tunica muscularis in an elderly subject may be substantially thickened, especially in the lower leg. The distribution and structure of the vessels differ according to body region.

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Vascular plexuses are situated at the subcutis-dermis transition : the cutaneous venous networks. As coils of sweat glands, surrounded by fatty tissue, are found at this level, the latter is known as the vasoglandular layer. From this arterial net the candelabra arteries originate, extending in an arc to the mid dermis and formis anastomoses there.

This results in another vascular network in the middermis, from which finer vessels branch off and form a third network at the level of the stratum subpapillare. From this capillaries extend into the papillary layer of the dermis enclosed by the epithelial ridges. The cutaneous vascular network represents a retrograde supply to parts of the fatty tissue, thus causing secondary involment of the deeper fatty tissue in pathologic processes which occur in the vessels situated higher, at the margins of the dermis, but through which the blood flows firs. The blood vessels of the hair follicles and the sweat glands are relatively independent; the lower and upper parts of the hair follicles area supplied by different vessels