• Stratum corneum: outer layer of the epidermis
  • Consists of dead (anuclear), keratin-filled cells
  • This layer is constantly being sloughed off.
• Stratum lucidum: thin, translucent layer
  • Located only on thick skin (palms and soles)
  • Composed of a homogeneous layer of keratinocytes with no nuclei or organelles
• Stratum granulosum: also called the granular layer
  • Contains keratohyalin
  • This layer has waterproof properties.
• Stratum spinosum
  • Composed of actively dividing keratinocytes with spinous-like projections (prickle cells)
  • This layer produces keratin and induces keratinization.
  • Langerhans cells are also located in this layer.
  • If undergoes malignant changes, will lead to cSCC
• Stratum basale (also called the basal cell layer of the epidermis)
  • Stem cells of the epidermis (their daughter cells migrate upwards and differentiate into other cells)
  • Melanocytes and Merkel cells are also located in this layer.
  • The stratum basale is regenerative (basal keratinocytes proliferate to fill skin defects).

Dermatopathology

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Histopathologic finding	Characteristics	Examples of associated conditions
Acantholysis	Separation of epidermal cells due to dissolution of intercellular bridges (e.g., desmosomes)	Pemphigus vulgaris
Acanthosis	Epidermal hyperplasia of the stratum spinosum	Acanthosis nigricans, Psoriasis
Hypergranulosis	Thickening of the stratum granulosum	Lichen planus
Hyperkeratosis	Thickening of the stratum corneum	Psoriasis, Calluses
Parakeratosis	Retention of nuclei in the stratum corneum	Psoriasis, Actinic keratosis
Spongiosis	Intraepidermal and intercellular edema	Eczematous dermatitis, Atopic dermatitis, Allergic contact dermatitis
Dyskeratosis	Premature keratinization of the stratum granulosum	Squamous cell carcinoma