Skin

Looks like

The largest organ: about 2 m² and 4 kg of layered barrier, renewed every month.

What it does

Keeps water in and germs out, senses touch, makes vitamin D and controls temperature.

Keeping it well

Sunburn is the exposure most clearly tied to melanoma. Sunscreen cuts squamous-cell cancer in trials; the melanoma evidence is thinner. The same light makes vitamin D; short exposure without burning is enough for that. A mole that changes shape, colour or bleeds needs looking at.

Its parts

• Epidermis
• Dermis
• Hypodermis

Related conditions

• Acne vulgaris
• Alopecia (androgenetic & areata)
• Atopic dermatitis (eczema)
• Blepharitis & styes
• Body dysmorphic disorder
• Boils and folliculitis
• Botulism
• Bullous pemphigoid
• Burns
• Candida & fungal infection
• Cellulitis
• Chickenpox (varicella)
• Chilblains (pernio)
• Cold sores (herpes simplex)
• Contact dermatitis
• Endemic fungal infections (histoplasmosis, coccidioidomycosis)
• Epidermoid (sebaceous) cyst
• Fibromyalgia
• Frailty & falls in older age
• Fungal skin infection (tinea)
• Hand, foot and mouth disease
• Heat exhaustion & heatstroke
• Hidradenitis suppurativa
• Hyperhidrosis
• Hypermobility and Ehlers–Danlos syndromes
• Hypothermia & frostbite
• Infantile haemangioma (strawberry mark)
• Kaposi sarcoma
• Keloid & hypertrophic scars
• Leishmaniasis
• Leprosy (Hansen's disease)
• Lichen planus
• Lichen sclerosus
• Lipoma
• Lyme disease
• Malnutrition & refeeding syndrome
• Mast cell activation & mastocytosis
• Measles
• Melanoma
• Melasma
• Mpox (monkeypox)
• MRSA and resistant staph infection
• Muscular dystrophy
• Nappy (diaper) rash
• Necrotising fasciitis
• Onchocerciasis (river blindness)
• Osteogenesis imperfecta (brittle bone disease)
• Parvovirus B19 (fifth disease)
• Pemphigus vulgaris
• Pilonidal sinus
• Pityriasis rosea
• Polymyalgia rheumatica
• Pressure ulcers & chronic wounds
• Psoriasis
• Psoriatic arthritis
• Radiation injury
• Rhabdomyolysis
• Rosacea
• Roseola (sixth disease)
• Rubella (German measles)
• Sarcoma
• Sarcopenia
• Scabies & lice
• Scarlet fever
• Scrub typhus & rickettsial infections
• Seborrhoeic dermatitis & dandruff
• Seborrhoeic keratosis
• Shingles (herpes zoster)
• Skin cancer (basal cell & squamous cell)
• Stevens–Johnson syndrome / toxic epidermal necrolysis
• Sun damage & actinic keratosis
• Systemic lupus erythematosus
• Systemic sclerosis (scleroderma)
• Tetanus
• Toxic shock syndrome
• Urticaria & angioedema
• Vitamin D deficiency
• Vitiligo
• Warts, molluscum and skin infections