Skin examination, dermoscopy and describing a rash
A first-time guide to skin examination: describing lesions and distributions, dermoscopy, bedside tests, biopsy choice and differential diagnosis.
Checked against sourcesVerified 31 October 2026
Dermatology
Diseases of the skin, hair and nails.
Introduction
Dermatology covers diseases of the skin, hair and nails. Most diagnoses are made by looking: the type of lesion, where it sits, how it is arranged and how fast it appeared. A rash that is also painful, blistering, or comes with fever or mucosal involvement is a different problem from a quiet scaly patch.
This section starts with how to examine skin and use basic treatments, then inflammatory and reactive disease, infections, pigment, hair and nail problems, and finally skin tumours.
Every topic uses the same layout: a short summary, what you should be able to do afterwards, the mechanism, the clinical picture, tests, treatment and the traps. Doses, thresholds and criteria are checked against named guidelines and shown with their source, because guidelines and countries sometimes differ.
How to study dermatology
Learn dermatology with one habit: describe the lesion before naming it. Primary lesion, distribution, surface change and colour narrow the list far faster than memorising pictures.
Learn the emergencies and the cancers: toxic epidermal necrolysis, necrotising fasciitis, severe drug reactions and melanoma, where a missed day or a missed biopsy changes the outcome. The check-yourself questions at the end of each topic test them a few days later.
Link this chapter to others: many rashes are signs of infection, autoimmune or malignant disease, and drug eruptions meet every specialty.
Contents by part
The topics below are in teaching order. Each part builds on the one before it.
- Examination and basic care. How to look at skin, describe a rash and use topical treatments and sun protection.
- Eczema, psoriasis and reactive skin disease. Inflammatory rashes, drug reactions and the blistering diseases.
- Atopic dermatitis
- Contact, seborrhoeic and stasis dermatitis
- Psoriasis
- Urticaria, angioedema and hypersensitivity reactions
- Drug eruptions, erythema multiforme and SJS/TEN
- Erythema nodosum and other reactive skin conditions
- Pemphigus vulgaris and bullous pemphigoid
- Acanthosis nigricans and lichen planus
- Rosacea and pityriasis rosea
- Skin infections and infestations. Viral, bacterial and fungal infections, parasites, acne and wound problems.
- Cutaneous viral infections: herpes, molluscum and warts
- Impetigo, cellulitis and necrotising fasciitis
- Fungal skin infections: tinea, candida, sporotrichosis
- Cutaneous larva migrans and other skin parasites
- Acne vulgaris, folliculitis and pilonidal disease
- Hidradenitis suppurativa, cysts and dermatofibroma
- Pressure ulcers and gangrene
- Pigment, hair, nails and systemic signs. Pigment loss, hair and nail disease and the skin signs of internal disease.
- Skin tumours. Premalignant lesions, benign growths, skin cancers and cutaneous lymphoma.
Topics
Topical therapy: emollients and corticosteroids
Simple steps for choosing emollients and topical corticosteroids, measuring fingertip units, avoiding fire risk and knowing when to refer.Checked against sourcesVerified 31 October 2026Sun protection, sunburn and seborrhoeic keratosis
How ultraviolet radiation damages skin, how to prevent sunburn and protect vitamin D, and how seborrhoeic keratosis presents and is managed.Checked against sourcesVerified 1 November 2026Skin in children and common paediatric rashes
Common skin problems in children: nappy rash, cradle cap, haemangiomas, viral rashes, birthmarks, impetigo, head lice and molluscum.Checked against sourcesVerified 31 October 2026Atopic dermatitis
Chronic, relapsing, itchy inflammation of the skin: barrier failure, Th2 inflammation, diagnosis, stepwise treatment, and complications such as eczema.Checked against sourcesVerified 1 November 2026Contact, seborrhoeic and stasis dermatitis
Irritant and allergic contact dermatitis, seborrhoeic dermatitis, and stasis dermatitis: diagnosis, patch testing, and treatment.Checked against sourcesVerified 1 November 2026
Psoriasis
How plaque psoriasis presents and how plaque, guttate, pustular and erythrodermic forms differ; how PASI scores severity and how guidelines treat it.Checked against sourcesVerified 1 November 2026Urticaria, angioedema and hypersensitivity reactions
Urticaria and angioedema: classification of hypersensitivity (Gell and Coombs I-IV), acute and chronic urticaria, histaminergic and bradykinin angioedema.Checked against sourcesVerified 1 November 2026Drug eruptions, erythema multiforme and SJS/TEN
How to recognise common drug rashes and tell erythema multiforme, DRESS, and SJS or TEN from benign eruptions, and how to manage them.Checked against sourcesVerified 1 November 2026Erythema nodosum and other reactive skin conditions
Tender inflammatory skin reactions that flag an underlying infection, sarcoidosis, bowel disease or drug trigger; covers erythema nodosum, pyoderma.Checked against sourcesVerified 1 November 2026Pemphigus vulgaris and bullous pemphigoid
Pemphigus vulgaris and bullous pemphigoid: how intraepidermal and subepidermal blistering differ, how to diagnose them, and how to treat following current.Checked against sourcesVerified 1 November 2026Acanthosis nigricans and lichen planus
Two dermatology topics: velvety flexural hyperpigmentation linked to insulin resistance, and lichen planus with its six Ps, Wickham striae and oral forms.Checked against sourcesVerified 1 November 2026Rosacea and pityriasis rosea
Rosacea and pityriasis rosea: definitions, diagnosis, treatment and differentials for two common dermatoses.Checked against sourcesVerified 1 November 2026Cutaneous viral infections: herpes, molluscum and warts
Cutaneous herpes, molluscum and warts: presenting features, diagnosis, management and prevention.Checked against sourcesVerified 1 November 2026Impetigo, cellulitis and necrotising fasciitis
Recognise, treat and prevent impetigo, cellulitis and erysipelas, and act fast on necrotising fasciitis, with antibiotic choices and surgical guidance.Checked against sourcesVerified 1 November 2026Fungal skin infections: tinea, candida, sporotrichosis
Fungal skin infections summarised and treated: tinea versicolor, dermatophytosis by site, cutaneous candidiasis and sporotrichosis.Checked against sourcesVerified 1 November 2026Cutaneous larva migrans and other skin parasites
Parasitic and zoonotic skin infestations: cutaneous larva migrans, scabies, head and body lice, tungiasis, and their treatment and prevention.Checked against sourcesVerified 1 November 2026Acne vulgaris, folliculitis and pilonidal disease
How acne develops and how folliculitis and pilonidal disease differ in cause, treatment and prevention.Checked against sourcesVerified 1 November 2026Hidradenitis suppurativa, cysts and dermatofibroma
HS, epidermal cysts, eyelid lesions, dermatofibroma, ichthyosis vulgaris and ageing skin: recognition, staging and management.Checked against sourcesVerified 1 November 2026Pressure ulcers and gangrene
How unrelieved pressure and ischaemia damage skin and soft tissue, how pressure injuries are staged and prevented, and how dry, wet and gas gangrene are.Checked against sourcesVerified 1 November 2026Vitiligo and disorders of pigmentation
How autoimmune melanocyte loss causes vitiligo, how to diagnose it with Wood's lamp, and guideline-based treatment including ruxolitinibChecked against sourcesVerified 1 November 2026Hair and nail disorders
Common hair and nail problems seen in clinic, from alopecia areata and androgenetic loss to fungal nails and systemic nail signs, and how to treat them.Checked against sourcesVerified 31 October 2026Skin signs of systemic disease
How the skin announces systemic disease: pruritus workup, erythroderma, paraneoplastic signs, organ and connective tissue signs, vasculitis.Checked against sourcesVerified 31 October 2026Actinic keratosis and premalignant skin lesions
Actinic keratosis and other premalignant skin and mucosal lesions: Bowen disease, keratoacanthoma, leukoplakia and field cancerisation.Checked against sourcesVerified 31 October 2026Benign skin tumours and naevi
Benign skin tumours and naevi: recognition, dermoscopy and excision of common lesions.Checked against sourcesVerified 31 October 2026Basal cell carcinoma, squamous cell carcinoma and Merkel
How BCC, SCC and Merkel cell carcinoma present, are risk-stratified and excised, and when radiotherapy and systemic therapy are used.Checked against sourcesVerified 31 October 2026Melanoma
Clinical melanoma primer: ABCDE and ugly duckling, dermoscopy, subtypes, AJCC 8 staging from Breslow thickness, margins and sentinel node, adjuvant.Checked against sourcesVerified 31 October 2026Cutaneous lymphoma, Kaposi sarcoma and vascular lesions
Cutaneous T-cell lymphoma (MF, Sezary syndrome), HHV-8 Kaposi sarcoma in HIV and benign vascular lesions: diagnosis, staging and treatment.Checked against sourcesVerified 1 November 2026