Structure and function of skin, hair and nails, and changes with age
The layers of the epidermis and dermis and the adhesion proteins that blistering diseases target, the stratum corneum barrier and filaggrin, UV damage and vitamin D synthesis, hair cycle and nail growth with worked timings, topical drug absorption, and what intrinsic ageing and photoageing do to each layer.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Skin is the largest organ, about 1.8 m² in an adult. Three layers: epidermis (keratinocytes, avascular), dermis (collagen, vessels, nerves, adnexa) and subcutis (fat).
- Its functions: barrier to water loss, microbes and chemicals; thermoregulation; immune surveillance; sensation; vitamin D synthesis; and UV protection by melanin.
- The proteins that hold it together are the targets in blistering disease, so knowing which layer splits predicts the clinical picture.
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Sources
- Rook's Textbook of Dermatology (10th ed.)Wiley-Blackwell (Griffiths, Barker, Bleiker, Hussain, Simpson, 2024), 2024
- DermNet: skin structure and function; ageing skin; Beau linesDermNet (New Zealand), accessed November 2026
- Cancer Council Australia: SunSmart and the UV indexAU/NZCancer Council Australia, accessed November 2026
- Palmer CNA et al. Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis. Nat Genet 2006;38:441-6Nature Genetics, 2006
- MacLaughlin J, Holick MF. Aging decreases the capacity of human skin to produce vitamin D3. J Clin Invest 1985;76:1536-8Journal of Clinical Investigation, 1985
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Deploy to Cloudflare on push to main