Dermatology: Skin basics, eczema and psoriasis

• Skin basics: Skin Structure and Function | Dermatological History and Examination | Describing Skin Lesions | Emollients and Topical Treatments | Topical Corticosteroids
• Eczema (dermatitis): Atopic Eczema | Treating Atopic Eczema | Severe Eczema and Systemic Treatment | Contact Dermatitis | Seborrhoeic Dermatitis | Other Types of Eczema
• Psoriasis and papulosquamous rashes: Psoriasis | Types of Psoriasis | Treating Psoriasis — Topical | Treating Psoriasis — Phototherapy and Systemic | Lichen Planus | Pityriasis Rosea and Other Scaly Rashes
• Revision: Drug Reference Table | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🧴 Skin basics, eczema and psoriasis — skin problems make up about 1 in 5 GP consultations. Most are managed in primary care with emollients and topical corticosteroids used correctly. Learn to describe a rash accurately — it's the key to diagnosis and referral. Eczema and psoriasis are chronic, relapsing conditions that affect quality of life, sleep and mental health as much as the skin.
Your four questions for every patient: What does the lesion or rash look like (type, colour, distribution)? Is it itchy, painful or infected? Is it affecting sleep, work, school or mood? Is the patient using treatments correctly and in enough quantity?

Skin Structure and Function

• Epidermis — outer layer of keratinocytes (renewed about every 4 weeks); contains melanocytes (pigment), Langerhans cells (immune) and Merkel cells (touch). The stratum corneum forms the barrier.
• Dermis — collagen and elastin; blood vessels, nerves, hair follicles, sweat and sebaceous glands.
• Subcutis — fat; insulation and energy store.
• Functions — barrier (water loss, infection, UV), temperature control, sensation, vitamin D synthesis, immunity, appearance and communication.
• Skin failure — widespread skin disease (erythroderma, TEN) causes fluid and protein loss, hypothermia, infection and high-output heart failure (see the Urticaria, Drug Reactions and Emergencies chapter).
• Skin of colour — redness (erythema) may look purple, brown or grey rather than red; post-inflammatory hyper- or hypopigmentation is common; keloids are more common. Learn to recognise conditions on all skin tones.

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Dermatological History and Examination

• History:
  • Onset, duration, site of first lesion, spread, change over time.
  • Symptoms — itch (and night itch), pain, bleeding, discharge.
  • Triggers — sunlight, heat, contact (work, hobbies, cosmetics, jewellery), foods, stress, infection.
  • Treatments tried — what, how much, how often, and the effect.
  • Drug history — new medicines in the last 2 months (drug eruptions).
  • Past and family history — atopy (asthma, hay fever), psoriasis, skin cancer.
  • Social — occupation, travel, contacts with similar rash (scabies, infections), sun exposure, sunbeds.
  • Impact — sleep, work, school, relationships, mood (Dermatology Life Quality Index).
  • Systemic symptoms — fever, joint pains, weight loss.
• Examination:
  • Good light; examine all the skin (including scalp, nails, mouth, genitals, soles) with consent and a chaperone.
  • Distribution — symmetrical, flexural, extensor, sun-exposed, dermatomal, follicular.
  • Morphology — describe the lesions (see below).
  • Palpate — texture, temperature, tenderness, blanching.
  • Dermoscopy for pigmented and suspicious lesions.
  • Lymph nodes and a general examination when relevant.
• Investigations — skin swabs (bacteria, viruses), skin scrapings, nail clippings and hair for fungal microscopy and culture, Wood's lamp, patch testing (contact allergy), skin biopsy (punch, shave, incisional, excisional), bloods for systemic disease.

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Describing Skin Lesions

• Useful signs:
  • Koebner phenomenon — lesions appear at sites of injury (psoriasis, lichen planus, vitiligo, warts).
  • Nikolsky sign — gentle pressure shears off the epidermis (pemphigus, SJS/TEN, staphylococcal scalded skin).
  • Auspitz sign — pinpoint bleeding when psoriatic scale is removed.
  • Dermographism — wheals where the skin is stroked (urticaria).
• Describe in order — site and distribution, number, size, shape, colour, surface (scale, crust), border, texture, surrounding skin. E.g. "multiple well-demarcated salmon-pink plaques with silvery scale on the elbows and knees".

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Emollients and Topical Treatments

• Emollients (moisturisers) — the foundation of treatment for dry skin, eczema and psoriasis:
  • Ointments (greasy) — most effective, no preservatives (fewer allergies); good for very dry skin.
  • Creams — less greasy, more acceptable in the day; contain preservatives.
  • Lotions and gels — light; for hairy areas and mild dryness.
  • Apply generously and often (at least twice daily), smoothing in the direction of hair growth; use as a soap substitute.
  • Quantities — adults may need 500 g a week; children 250–500 g a week.
  • Fire risk (MHRA) — all emollients (paraffin-based and paraffin-free) soak into clothing and bedding and make them flammable — warn about naked flames and smoking.
  • Apply emollient and topical steroid at different times (ideally about 30 minutes apart).
• Choosing a vehicle — ointments for dry, scaly skin; creams for moist or weeping areas; lotions, gels, foams or shampoos for the scalp and hairy areas.
• Other topical treatments — calcineurin inhibitors (tacrolimus, pimecrolimus), vitamin D analogues (calcipotriol), coal tar, salicylic acid (removes scale), dithranol, retinoids, antimicrobials, antifungals.
• Adherence — topical treatment is time-consuming; explain how much, how often and for how long; give written plans; under-treatment is very common.

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Topical Corticosteroids

• Fingertip unit (FTU) — the amount squeezed from the tip of an adult index finger to the first crease (about 0.5 g) — covers an area of two adult palms.
• How to use — usually once daily (as effective as twice); use the lowest potency that works; treat flares early and firmly, then step down; "weekend therapy" (twice weekly to frequently flaring areas) can prevent relapses.
• Local side effects — skin thinning (atrophy), striae, telangiectasia, easy bruising, perioral dermatitis, worsening of rosacea and acne, masking of fungal infection (tinea incognito), hypopigmentation, glaucoma and cataract (around the eyes).
• Systemic side effects — rare; adrenal suppression with large amounts of potent steroids, especially in infants or under occlusion.
• Topical steroid withdrawal (MHRA) — rare reactions (redness, burning, skin peeling) after stopping long-term moderate to high potency steroids; reduce gradually after long use.
• Steroid phobia — fear of side effects causes under-treatment; reassure that correctly used topical steroids are safe and effective.
• Combination products — with antimicrobials (e.g. fusidic acid) or antifungals for short-term use in infected eczema or intertrigo.

💡 Clinical Pearl: Most "treatment failure" in eczema is under-treatment — too little emollient, too weak a steroid, or stopping too soon. Prescribe enough (500 g of emollient a week for an adult), explain fingertip units, and give a written plan.

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Atopic Eczema

• What it is: A chronic, itchy, inflammatory skin condition with a defective skin barrier (often filaggrin gene mutations) and immune dysregulation. Affects about 1 in 5 children and 1 in 10 adults; part of the "atopic march" with food allergy, asthma and hay fever.
• Features:
  • Itch (the key symptom) — scratching worsens the rash ("itch–scratch cycle"); poor sleep.
  • Dry skin; red, ill-defined patches; papules, vesicles, weeping and crusting when acute; lichenification when chronic.
  • Distribution by age:
    • Infants — face (cheeks), scalp, extensor surfaces; nappy area usually spared.
    • Children and adults — flexures (elbow and knee creases), neck, wrists, ankles; hands; face and eyelids in adults.
  • In skin of colour — may look darker, follicular (bumpy), with marked pigment change.
• Diagnosis — clinical: itchy skin plus three or more of: flexural involvement (or cheeks under 4), history of dry skin, personal or family atopy, visible flexural eczema, onset under 2.
• Triggers — soaps and detergents, heat, sweating, wool, infections, stress, house dust mite, pets, pollen, hormones; food allergy (mainly in infants with severe early eczema — cow's milk, egg, peanut).
• Severity — clear, mild, moderate, severe (by appearance, itch and impact); assess quality of life and psychological effects.
• Complications:
  • Bacterial infection (Staph aureus) — weeping, crusting, pustules, rapid worsening.
  • Eczema herpeticum (herpes simplex) — an emergency: rapidly spreading, painful, clustered "punched-out" erosions or vesicles, fever — urgent oral or IV aciclovir; same-day referral; ophthalmology if around the eyes.
  • Sleep loss, behavioural and mood problems, bullying, time off school or work.

⚠️ Safety Pearl: A child with eczema who suddenly gets worse with painful, clustered punched-out sores and fever has eczema herpeticum until proven otherwise. Start aciclovir straight away and refer the same day — it can spread to the eyes and become life-threatening.

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Treating Atopic Eczema

• Stepped approach (NICE CG57 for children; same principles in adults) — step up for flares, step down when controlled:
  • Emollients for everyone — liberally and often, including when clear; soap substitute.
  • Mild eczema — mild topical steroid (hydrocortisone 1%).
  • Moderate eczema — moderate topical steroid (clobetasone butyrate) for the body; mild for the face.
  • Severe eczema — potent topical steroid (betamethasone valerate) for the body (not the face or neck; specialist advice under 12 months); short courses (up to 7–14 days for flares).
  • Face and flexures — mild steroids or short courses of moderate; topical calcineurin inhibitors (tacrolimus from age 2, pimecrolimus) as a second-line, steroid-sparing option — burning at first; sun protection.
  • Prevent flares — twice-weekly topical steroid or tacrolimus to problem areas.
• Infected eczema — flucloxacillin (clarithromycin if penicillin allergic) for widespread infection; topical antiseptics or short topical antibiotics for small areas; replace contaminated emollient tubs.
• Itch — non-sedating antihistamines if urticaria or severe itch; a sedating antihistamine for 1–2 weeks for sleep in a flare (over 6 months); keep nails short; cotton clothing.
• Bandages and wet wraps — for severe eczema, under specialist advice.
• Food allergy — consider in infants with moderate to severe eczema not controlled, or immediate reactions to food; don't start exclusion diets without dietetic or allergy advice.
• Education — written action plan; eczema nurse; school involvement; National Eczema Society resources.
• Refer to dermatology — diagnostic uncertainty, not controlled despite optimal treatment, recurrent infections, suspected contact allergy, severe impact, eczema herpeticum (urgent).

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Severe Eczema and Systemic Treatment

• Phototherapy — narrowband UVB.
• Conventional systemic immunosuppressants — ciclosporin (fast-acting; kidney function and BP), methotrexate (weekly, with folic acid; FBC and LFTs), azathioprine (check TPMT first), mycophenolate.
• Short oral steroid courses — avoid where possible (rebound flare).
• Biologics — dupilumab (anti-IL-4/IL-13; conjunctivitis is common), tralokinumab and lebrikizumab (anti-IL-13) — for moderate to severe eczema when systemic treatment has failed or is unsuitable (NICE-approved).
• Oral JAK inhibitors — abrocitinib, upadacitinib, baricitinib — effective; MHRA advice: use in people over 65, smokers, or those with cardiovascular or cancer risk factors only if no suitable alternative (risk of MACE, VTE, cancer, serious infection).
• Monitoring — screen for TB, hepatitis B and C, HIV before immunosuppressants; vaccinations (avoid live vaccines on some agents).

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Contact Dermatitis

• Irritant contact dermatitis (the commonest) — direct damage from irritants:
  • Wet work (hand washing, cleaning, hairdressing, healthcare, catering), detergents, solvents, friction.
  • Hands — dry, cracked, red, sore skin (backs of hands and finger webs).
  • Anyone exposed enough; worse in people with atopic eczema.
• Allergic contact dermatitis — type IV (delayed) hypersensitivity in sensitised people, 24–72 hours after contact:
  • Common allergens — nickel (jewellery, belt buckles, jean studs), fragrances, preservatives (e.g. methylisothiazolinone in wipes, cosmetics), hair dye (PPD — severe scalp and face swelling; "black henna" tattoos), rubber accelerators (gloves), chromate (cement), acrylates (nail products), topical medicines (neomycin, local anaesthetics, steroids), plants.
  • Shape and site match the contact — earlobes (earrings), wrist (watch), eyelids (nail varnish transferred by fingers), face (cosmetics).
  • Patch testing to identify the allergen.
• Management — identify and avoid the cause; protective gloves (cotton liners under nitrile); emollients and soap substitutes; topical steroids (potent for hands); occupational — occupational health, workplace adjustments; reportable occupational disease in some cases.
• Chronic hand eczema — if severe and not responding — specialist: alitretinoin (teratogenic), phototherapy, systemic treatment, delgocitinib cream (newer).

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Seborrhoeic Dermatitis

• What it is: A common, chronic inflammatory rash linked to Malassezia yeasts, in sebum-rich areas.
• Adults — red, greasy, yellowish scale on the scalp (dandruff), eyebrows, nasolabial folds, behind the ears, eyelids (blepharitis), central chest and back; worse with stress and in winter.
• Infants — "cradle cap" (yellow, greasy scale on the scalp) and nappy area in the first months; not itchy; settles by 6–12 months — emollient and gentle brushing, mild steroid or imidazole cream if needed.
• Severe or sudden seborrhoeic dermatitis — think of HIV, Parkinson's disease, alcohol misuse, depression.
• Treatment:
  • Scalp — ketoconazole 2% shampoo (twice weekly, leave on 5 minutes), selenium sulfide, coal tar; salicylic acid for thick scale; potent steroid scalp application for short flares.
  • Face and body — ketoconazole 2% cream; mild steroid (hydrocortisone 1%) short term; topical calcineurin inhibitors.
  • Relapses are common — maintenance antifungal shampoo.

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Other Types of Eczema

• Discoid (nummular) eczema — coin-shaped, itchy, well-defined plaques (often on legs); may weep; mistaken for tinea or psoriasis; potent steroid ± antiseptic; emollients.
• Pompholyx (dyshidrotic eczema) — intensely itchy deep-seated vesicles on the palms, sides of fingers and soles; triggered by heat, sweating, stress, contact allergens; potent steroid, soaks (potassium permanganate), avoid irritants.
• Venous (gravitational, stasis) eczema — lower legs with venous hypertension: itchy, scaly, pigmented (haemosiderin), varicose veins, oedema, lipodermatosclerosis ("inverted champagne bottle" legs); risk of ulcers. Emollients, topical steroids, compression (after checking ABPI), leg elevation; refer for vein assessment; allergic contact dermatitis to topical medicines is common.
• Asteatotic eczema (eczema craquelé) — older people; dry, "crazy-paving" cracked skin on the shins; worse in winter and with hot baths; emollients and mild steroids.
• Lichen simplex chronicus — a localised thick, lichenified plaque from repeated scratching (neck, ankles, genitals); potent steroid under occlusion; break the itch–scratch cycle.
• Juvenile plantar dermatosis — shiny, cracked skin on the front of the feet in children (sweaty trainers); cotton socks, emollients.
• Nappy rash — irritant (spares skin folds) versus candida (involves folds, satellite lesions) — barrier cream, nappy-free time; imidazole cream for candida.

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Psoriasis

• What it is: A chronic, immune-mediated inflammatory disease with rapid keratinocyte turnover (IL-17 and IL-23 pathways). About 2% of people; peaks in the 20s and 50s; strong genetic component (HLA-Cw6).
• Chronic plaque psoriasis (about 90%):
  • Well-demarcated, salmon-pink (or purple, grey or dark brown in skin of colour) plaques with silvery-white scale.
  • Sites — extensor surfaces (elbows, knees), scalp (and hairline, behind ears), lower back, umbilicus, natal cleft, genitals.
  • Itchy in many; Koebner phenomenon; Auspitz sign.
• Nail psoriasis (in about half; more with psoriatic arthritis) — pitting, onycholysis (nail lifting), "oil drop" or "salmon patch" discolouration, subungual hyperkeratosis, nail dystrophy.
• Triggers and aggravating factors:
  • Infection — streptococcal sore throat (guttate psoriasis), HIV.
  • Drugs — lithium, beta-blockers, antimalarials (hydroxychloroquine, chloroquine), NSAIDs, ACE inhibitors, withdrawal of oral steroids (can trigger pustular psoriasis), immune checkpoint inhibitors.
  • Stress, alcohol, smoking, obesity, skin trauma, cold weather.
• Comorbidities (assess and manage):
  • Psoriatic arthritis (up to 1 in 3) — screen every year with the PEST questionnaire; refer to rheumatology if positive.
  • Cardiovascular disease and metabolic syndrome (obesity, diabetes, hypertension, dyslipidaemia) — especially in severe psoriasis.
  • Depression and anxiety; alcohol misuse.
  • IBD (Crohn's disease), non-alcoholic fatty liver disease, uveitis.
• Severity — body surface area, PASI (Psoriasis Area and Severity Index), DLQI, physician's assessment.

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Types of Psoriasis

⚠️ Safety Pearl: Avoid oral steroids in psoriasis. They may clear it briefly, but stopping them can trigger severe generalised pustular or erythrodermic psoriasis — a dermatological emergency.

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Treating Psoriasis — Topical

• General — emollients (reduce scale and itch); explain the chronic course; stop smoking, reduce alcohol, weight loss; screen for comorbidities.
• Trunk and limbs (NICE CG153):
  • First-line — a potent corticosteroid once daily plus a vitamin D analogue (calcipotriol) once daily, applied at different times of day, for up to 4 weeks (or a combined product — calcipotriol with betamethasone, e.g. Dovobet, Enstilar foam).
  • If not improved after 8 weeks — vitamin D analogue twice daily.
  • Then — potent steroid twice daily (up to 4 weeks) or coal tar preparation.
  • Breaks of 4 weeks between courses of potent steroids; avoid very potent steroids for more than 4 weeks.
• Scalp — potent steroid (lotion, shampoo or foam) for up to 4 weeks; descale first if thick (salicylic acid, coconut oil, coal tar); then combined calcipotriol–betamethasone.
• Face, flexures and genitals — mild or moderate steroid for 1–2 weeks (thin skin); topical calcineurin inhibitors (off-label) for longer control.
• Others — dithranol (short contact; stains), salicylic acid, topical retinoids (tazarotene).
• Review — 4 weeks after starting a new treatment (adults); show patients how much to apply.

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Treating Psoriasis — Phototherapy and Systemic

• Refer to dermatology — diagnostic uncertainty, extensive or severe disease, not controlled with topical treatment, major impact on life, generalised pustular or erythrodermic psoriasis (urgent), nail disease with functional problems.
• Phototherapy — narrowband UVB (2–3 times a week); PUVA (psoralen plus UVA) for resistant disease; long-term skin cancer risk (cumulative dose).
• Standard systemic drugs:
  • Methotrexate (weekly) — first-line; folic acid on a different day; FBC, U&E, LFTs monitoring; liver fibrosis (PIIINP or FibroScan), pneumonitis; teratogenic; avoid trimethoprim and co-trimoxazole (bone marrow toxicity).
  • Ciclosporin — rapid control; nephrotoxicity, hypertension; short-term use.
  • Acitretin (oral retinoid) — pustular psoriasis; highly teratogenic — avoid pregnancy for 3 years after stopping; dry lips and skin, raised lipids and LFTs.
  • Apremilast (PDE4 inhibitor), deucravacitinib (TYK2 inhibitor), dimethyl fumarate — oral options.
• Biologics (NICE TAs — for severe psoriasis, e.g. PASI 10 or more and DLQI over 10, not responding to or unsuitable for standard systemic therapy):
  • TNF inhibitors — adalimumab, etanercept, infliximab, certolizumab.
  • IL-17 inhibitors — secukinumab, ixekizumab, brodalumab, bimekizumab (also IL-17F).
  • IL-12/23 and IL-23 inhibitors — ustekinumab, guselkumab, risankizumab, tildrakizumab.
  • Screen for TB, hepatitis B and C, HIV; avoid live vaccines; infection risk; IL-17 inhibitors can worsen IBD.

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Lichen Planus

• What it is: An immune-mediated inflammatory condition of skin, mouth, genitals, hair and nails; middle age.
• Skin features — the "5 Ps" — Purple, Polygonal, Planar (flat-topped), Pruritic Papules; fine white lines on the surface (Wickham's striae); Koebner phenomenon.
• Sites — flexor wrists, forearms, shins, lower back, genitals.
• Oral lichen planus — white lacy (reticular) patches on the inner cheeks; erosive forms are painful; small risk of oral squamous cell carcinoma — dental and oral review.
• Other — genital erosions (vulvovaginal–gingival syndrome), nail thinning and ridging (pterygium), scarring hair loss (lichen planopilaris), dark pigmentation in skin of colour.
• Lichenoid drug eruptions — ACE inhibitors, beta-blockers, thiazides, gold, antimalarials, NSAIDs, checkpoint inhibitors.
• Treatment — potent or very potent topical steroids; oral — steroid mouthwashes or pastes, avoid irritants; severe — oral steroids, acitretin, phototherapy, methotrexate; usually settles within 1–2 years (oral disease lasts longer). Check for hepatitis C in some cases.
• Lichen sclerosus — white, atrophic, itchy plaques of the genitals; very potent topical steroid; SCC risk (see the Pelvic Floor, Ovary and Vulva chapter).

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Pityriasis Rosea and Other Scaly Rashes

• Pityriasis rosea — common in teenagers and young adults; probably viral (HHV-6/7):
  • A single larger oval "herald patch" (often on the trunk), followed within 1–2 weeks by many smaller oval pink scaly patches along skin lines in a "Christmas tree" pattern on the back; fine "collarette" scale.
  • Mild itch; may have a preceding viral illness.
  • Self-limiting in 6–12 weeks; emollients, mild steroid or antihistamine for itch.
  • Exclude secondary syphilis if atypical (palms and soles involved, sexual risk) — serology.
  • In pregnancy — linked to slightly higher miscarriage risk in the first 15 weeks — inform the obstetric team.
• Pityriasis versicolor — see the Skin Infections chapter.
• Tinea corporis — annular, scaly, spreading edge with central clearing — scrape before treating with steroids.
• Keratosis pilaris — rough, follicular papules on the backs of the upper arms and thighs; common with atopy; emollients with urea or salicylic acid.
• Ichthyosis — inherited dry, fish-like scale (ichthyosis vulgaris — filaggrin; X-linked ichthyosis — boys); acquired ichthyosis can signal lymphoma or other systemic disease.
• Cutaneous lupus (discoid — scarring, sun-exposed) and mycosis fungoides (persistent patches in sun-protected areas) — consider biopsy for atypical or persistent scaly rashes.

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Drug Reference Table

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Spot the Diagnosis