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- Epidermis is stratified squamous keratinized with orderly maturation from basal → spinous → granular → cornified layers.
- Dermis contains adnexa (hair follicles, sebaceous and eccrine/apocrine glands), vessels, nerves, and variable collagen/elastic fibers.
- Papillary dermis has finer collagen and capillary loops; reticular dermis is thicker, coarser collagen.
- Subcutis is lobulated fat separated by fibrous septa with vessels and nerves.
- Basal layer p63+/CK5/6+, attached by hemidesmosomes; melanocytes and Merkel cells interspersed.
- Spinous layer with desmosomal “spines”; granular layer with keratohyalin granules; stratum corneum anuclear.
- Thickness and rete ridge pattern vary by site (thick acral skin vs thin eyelid).
- Infundibulum (opens to surface, keratinized), isthmus, and inferior segment (bulb with matrix, dermal papilla).
- Outer root sheath CK5/6+; inner root sheath trichohyalin+; matrix cells Ki-67 high near bulb.
- Arrector pili smooth muscle inserts at bulge region; sebaceous gland opens into infundibulum.
- Sebaceous: lobulated, foamy cytoplasm, holocrine secretion; EMA/CK7+, androgen responsive.
- Eccrine: secretory coil (pale glycogen-rich clear cells + darker myoepithelial rim) and straight duct segments; spiral intraepidermal duct (acrosyringium).
- Apocrine: larger lumen, decapitation secretion, located in axilla/groin/areola; ducts may keratinize near skin surface.
- Superficial vascular plexus in papillary dermis, deeper plexus at dermal–subcutis junction.
- Nerves and Meissner/Pacinian corpuscles depending on site; perineurium EMA+, S100 highlights Schwann cells.
