Skin examination, dermoscopy and describing a rash

• A systematic skin examination looks at the whole skin, hair, nails and mucosa, in good light, with the patient fully undressed and properly draped; missing a single area can mean missing a melanoma.
• Every rash should be described in a standard order: morphology, arrangement, distribution and configuration, then palpation findings and evolution over time.
• The purpose of the examination is not only to name a lesion but to separate primary lesions, which reveal the disease process, from secondary changes produced by scratching, infection or chronicity.
• Dermoscopy is a hand-held magnified view with polarised or immersion light; it refines the assessment of pigmented lesions and many inflammatory and infectious dermatoses.
• Bedside tests choose the diagnosis: potassium hydroxide preparation for fungi, Wood lamp for some fungi and pigment disorders, scrapings and patch testing for contact allergy, and a correctly chosen biopsy when tissue diagnosis is needed.
• Safety comes first: rapidly spreading, painful, blistering or mucosal rashes, or a rash with fever, need urgent medical assessment before any elective test.

By the end of this page you should be able to:

1. Perform and record a complete skin examination in a logical, reproducible order.
2. Name and define primary and secondary skin lesions and use distribution and configuration terms correctly.
3. Palpate a lesion properly and decide whether it is flat, raised, deep, firm, fluctuant or infiltrated.
4. Decide when dermoscopy, Wood lamp examination, a skin scraping, patch testing or a biopsy will help, and which biopsy technique to use.
5. Describe a rash in standard medical language and use that description to build a short, defensible differential diagnosis.
6. Recognise red flags that require urgent treatment rather than routine testing.

Skin examination is a physical examination in which the whole body surface is inspected and palpated, including hair, nails and mucous membranes. It is often the entire diagnosis in dermatology, because the skin is the only organ that can be seen in full without instruments. The examination is taught as a procedure because the quality of the result depends heavily on method: lighting, exposure, sequence and how findings are recorded.

This page is written for a student meeting the skin examination for the first time. It also assumes that a rash may be the first sign of a serious systemic illness, and that the examination is therefore part of general medicine, not only of dermatology.

A note on guideline editions used for this page: the European Society of Contact Dermatitis diagnostic patch testing guideline update of 2026 is used for patch testing practice; the StatPearls editions of 2023 and 2025 are used for biopsy technique, dermoscopy and Wood lamp examination; and the American Academy of Dermatology guidance reviewed in 2024 is used for the red-flag features of rashes. The British Association of Dermatologists, which produces clinical guidelines accredited by NICE, publishes them free of charge in the British Journal of Dermatology.^[7]

Skin examination is indicated whenever a patient presents with a visible skin problem, but also in several less obvious situations:

• A rash, mole or pigmented lesion that is new, changing, bleeding or not healing.
• Pruritus, pain or discomfort that the patient locates on the skin, even when nothing is visible initially.
• Suspected infection of skin, hair or nails, including fungal and viral infections.
• Suspected allergic or irritant contact dermatitis, or any drug eruption.
• Systemic disease that may present in the skin, such as lupus erythematosus, vasculitis, infective endocarditis or a nutritional deficiency.
• Staging and monitoring of a known skin disease, including response to treatment.
• Surveillance of patients at high risk for skin cancer, such as those with many naevi, fair skin, past skin cancer or significant ultraviolet exposure.
• Baseline examination before phototherapy, immunosuppressive therapy or other treatments that alter skin or immune function.

There is no absolute contraindication to looking at the skin. The cautions are practical:

• If the patient is acutely unwell, examine the skin before any other test, because the rash may explain the illness.
• Postpone a detailed cosmetic examination if the patient is in pain, but never omit inspection of mucosa in a patient with a drug eruption.
• Patch testing should be postponed in severe or generalised active dermatitis, in patients on high-dose systemic immunosuppression where withdrawal is planned, when the planned test sites are affected by dermatitis, and in many cases during pregnancy and lactation.
• Bedside tests must never delay treatment of rapidly spreading infection, suspected Stevens–Johnson syndrome or toxic epidermal necrolysis, purpura with fever, or airway involvement.

The skin has three layers relevant to examination. The epidermis is the thin outer barrier; lesions that alter it change colour, scale or surface. The dermis contains vessels, nerves and appendages; lesions here are usually palpable and may be tender or infiltrated. The subcutis and deeper structures produce nodules, tethering or temperature change. Hair follicles, eccrine and apocrine glands, nails and mucous membranes are part of the skin organ and must be included.

Clinical assessment of a skin lesion asks five questions:

1. Is it localised or widespread?
2. What is its morphology (what it looks like before any secondary change)?
3. Where on the body is it (which regions, and which side)?
4. What does it feel like on palpation?
5. How has it changed with time?

Keep the kit simple and standardised so that every member of a team records the same findings:

• Good, well-focused light; daylight-equivalent artificial light is acceptable, but yellow room light worsens colour judgement.
• A hand lens or magnifying glass.
• A metric ruler and a marking pen for size and mapping.
• Non-sterile and sterile gloves.
• A Wood lamp in a darkened space.
• A dermatoscope (hand-held, with polarised and/or non-polarised contact mode) for pigmented and vascular lesions.
• Materials for skin scraping: scalpel blade, slides and coverslips, potassium hydroxide solution and a microscope where available.
• For biopsy: punch instruments in several sizes, local anaesthetic, fine sutures or adhesive strips, and specimen containers with formalin.
• A camera for serial photography with a scale in the frame.

Explain the procedure before undressing, because the examination can feel exposing. Examine in a private, warm room with a chaperone when required by local policy. Undressing is complete, with dignity preserved by a gown and uncovering one area at a time. The patient should remove makeup, nail varnish and sunscreen so that colour changes are visible. Inspect in a set order so that areas are not forgotten: front and back of trunk, upper limbs, lower limbs, hands and feet, scalp, nails, and mucosa.

Ask the patient to point out every concern, then examine beyond the area they indicate, because many important findings are not noticed by the patient.

Before touching the skin, step back. Decide whether the process is localised, regional or generalised, symmetric or asymmetric, and confined to sun-exposed, flexural, extensor, intertriginous, periorificial or acral sites. Distribution is often the most important clue to diagnosis.

Use distribution terms precisely:

• Generalised: most or all of the body, with or without mucosal involvement.
• Localised: a single area or a few discrete areas.
• Flexural: folds such as the antecubital and popliteal fossae, axillae and groin (eczema pattern).
• Extensor: elbows, knees, scalp and sacrum (psoriasis pattern).
• Acral: hands, feet and distal limbs.
• Dermatomal: a unilateral band following a sensory nerve territory, suggesting varicella zoster.
• Blaschkoid/linear: following embryonic skin lines, suggesting mosaicism.
• Symmetric versus asymmetric: symmetry suggests systemic or allergic processes; asymmetry often suggests external contact.
• Sun-exposed: face, neck, dorsal hands and forearms, V of the chest, suggesting photosensitivity or actinic disease.
• Intertriginous: skin folds, where friction, moisture and candida predominate.

Primary lesions are the first structural change produced by the disease itself. They should be recorded before scratching or secondary change obscures them.

Secondary lesions are produced from primary lesions by the patient or by time. They often hold the clue to chronicity and behaviour.

• Scale: flakes of stratum corneum, as in psoriasis or eczema.
• Crust: dried serum, blood or pus, as in impetigo.
• Erosion: shallow loss of epidermis that does not bleed and heals without scarring.
• Ulcer: full-thickness loss of epidermis and at least part of the dermis, healing with scar.
• Fissure: linear crack, common in chronic hand eczema and athlete's foot.
• Excoriation: scratch mark, often linear and uniform.
• Lichenification: thickened skin with accentuated markings from chronic rubbing.
• Atrophy: thinning of epidermis or dermis, with loss of skin lines or translucency.
• Scar: fibrous replacement; hypertrophic and keloid scars extend beyond or above the original wound.
• Maceration: softening and whitening from prolonged moisture.

Record arrangement as well as individual morphology. Useful configuration terms are annular (ring), polycyclic (merged rings), target (concentric rings, as in erythema multiforme), linear, serpiginous (snake-like), reticular (net-like), stellate (star-like), herpetiform (grouped vesicles), dermatomal, and zosteriform.

Inspection alone is incomplete. Palpate with a gloved finger or the back of the hand, comparing the lesion with normal skin beside it. Decide whether it is flat, papular or nodular; soft, firm or hard; tender or painless; warm or cool; fluctuant or solid; and whether the epidermis slides over it or is tethered. Palpation detects infiltration, which is invisible: an apparently flat erythematous patch that feels indurated may be an infiltrative process. It also distinguishes a cyst (fluctuant, with a thick wall) from a solid nodule, and identifies induration around a tumour or scleroderma.

Measure every lesion in millimetres with a ruler. For a suspicious pigmented lesion, record the longest diameter and the perpendicular diameter. Palpate regional lymph nodes when a lesion could be malignant or infected, and record generalised lymphadenopathy separately.

A complete description follows the same order in every patient, so that another clinician can visualise the rash without seeing it:

1. Site and distribution, including symmetry, region and any dermatomal or acral pattern.
2. Morphology of the primary lesion, using the terms above and an approximate size in millimetres.
3. Colour in the patient's skin tone, including erythema, brown, grey, violaceous or post-inflammatory change.
4. Surface and scale, including whether scale is fine, silvery, greasy or absent.
5. Arrangement and configuration, such as annular or grouped.
6. Borders: well-defined, ill-defined, active or advancing.
7. Palpation findings: flat or raised, tender, indurated, fluctuant, warm.
8. Mucosal, nail and hair findings, including subtle changes at these sites.
9. Temporal evolution: onset, spread, itch or pain, response to treatment, and any relation to drugs, foods, travel or contact.

Example of a well-formed description: "Symmetric, pruritic, well-demarcated erythematous plaques with silvery scale on the extensor surfaces of both knees, elbows and scalp, present for some weeks, with nail pitting." A reader can picture the rash and narrow the cause.

The description is the raw material for the differential. Organise possibilities by morphology first, then by time course and exposure history. A useful bedside method is:

• Ask whether the process is inflammatory, infectious, neoplastic, autoimmune or vascular, because each produces different patterns.
• Build a short list from the primary lesion and distribution, then remove each diagnosis that does not fit a defining feature.
• Look for mucosal lesions, nail changes and systemic symptoms, which narrow the list sharply.
• Always include drug eruption as a possibility for any new generalised rash, and take a full medication history including over-the-counter and herbal products.
• In an unwell patient, rank the differential by danger, not by likelihood: meningococcaemia, Stevens–Johnson syndrome, toxic epidermal necrolysis, cellulitis with sepsis and necrotising fasciitis all present in the skin.

A teaching algorithm works in four steps:

1. Name the primary lesion.
2. Map the distribution.
3. Add two or three discriminating features from history and palpation.
4. Decide whether the diagnosis is already clear, whether a bedside test will confirm it, or whether a biopsy is required.

Dermoscopy, also called epiluminescence or skin surface microscopy, is a non-invasive technique in which a lesion is viewed under magnification using either polarised light or immersion fluid. It was developed for suspicious melanocytic lesions, where it helps separate benign lesions, dysplastic naevi and melanoma, and for keratinocyte cancers such as basal cell carcinoma and squamous cell carcinoma. Its use has expanded steadily to inflammatory dermatoses, pigmentary disorders, infectious dermatoses, and diseases of the hair, scalp and nails. Specific names are used for these indications: pigmentaroscopy for pigmented lesions, trichoscopy for hair and scalp, onychoscopy for nails, inflammoscopy for inflammatory dermatoses, and entomodermoscopy for infestations and infections.^[1]

Basic technique matters more than memorising patterns:

• Use the same instrument and lighting each time so that findings are comparable.
• Allow the skin to settle after touching it, so that erythema from pressure is not mistaken for inflammation.
• Record whether contact with fluid and non-polarised light, or non-contact polarised light, was used, because the visual findings differ.
• Examine the lesion and its edge, comparing with a neighbouring normal area.
• Document with dermoscopic photography when it will be used for follow-up.

A beginner should learn the standard colour and structure vocabulary before attempting diagnostic algorithms: brown lines, dots, globules and a pigment network for melanocytic lesions; arborising vessels, ulceration and blue-grey ovoid nests for basal cell carcinoma; white structureless areas, polymorphic vessels and keratin for squamous cell carcinoma and keratoacanthoma. Inflammatory lesions show dotted vessels and coloured scale; scabies is recognised by the triangular "delta sign" at the end of a burrow. These patterns are learned under supervision and confirmed histologically when any doubt remains.

Wood lamp examination is not just shining a light. Done carefully, it gives real diagnostic information at the bedside.

• The device emits long-wave ultraviolet light.
• The examination room must be completely dark, because ambient light overwhelms the colour change.
• The affected skin is examined for fluorescence or colour change; normally the skin does not fluoresce and the light appears purple or violet.
• Wood lamp detects fluorescent metabolites in certain bacteria and fungi, including some dermatophytes, and can show inconspicuous scalp lesions; it is used to select infected skin and hairs for laboratory examination.
• It also reveals pigment disorders such as vitiligo, where affected skin appears strikingly white, and other irregularities of pigmentation.
• It can be used to look for a corneal abrasion on the surface of the eye.
• The test can be performed by any healthcare worker, but interpretation is most reliable when a dermatologist or experienced clinician performs it. It is a diagnostic, not a therapeutic, device.^[2]

Bedside sampling is often the cheapest and fastest step. It is most useful when the clinical picture suggests fungus, scabies or a simple infection.

• Potassium hydroxide preparation is the standard screen for dermatophyte and yeast. Scale from the active border of a lesion is scraped onto a slide, a coverslip is added, and a drop of potassium hydroxide is applied; gentle heating dissolves keratin and reveals branching hyphae. Nail clippings can be examined in the same way.
• Skin scraping for scabies uses a scalpel blade to scrape the roof of a burrow, with immersion oil or mineral oil, and examination under low power for the mite, eggs or faeces.
• Gram stain or culture is reserved for bacterial infection, particularly when there is purulence, an atypical site or treatment failure.
• Direct immunofluorescence and special stains are laboratory tests used in blistering disease and are not routine bedside procedures.

Document the site sampled and whether a negative result was obtained from adequate material, because sampling too little is the commonest cause of a false negative.

Patch testing is the standard investigation for contact allergy caused by delayed, type IV hypersensitivity.^[4] It aims to reproduce, under occlusion and in standardised conditions, the elicitation phase of allergic contact dermatitis. Allergens are applied to the skin, usually the upper back, and the results are read later, up to seven days after application so that late reactions are not missed. A positive reaction is interpreted with the clinical picture; contact allergy on its own is not a diagnosis and not all positives are relevant.

Four principles keep patch testing useful:

1. Test because of a compatible history and examination, not as a screening test for everyone. Indications include eczematous or non-eczematous dermatitis where contact allergy is suspected, chronic dermatitis that does not improve with treatment, skin or mucous membrane eruptions where delayed hypersensitivity is suspected, and suspected sensitisation to implant materials.
2. A baseline series of allergens should be applied in every patient investigated for contact allergy, because unsuspected allergens are common; the series is adjusted over time as exposures change and is complemented, rather than replaced, by allergens suggested by occupational and personal history.
3. Avoid testing during severe or generalised active dermatitis, on skin treated recently with topical corticosteroids or calcineurin inhibitors (an adequate washout for lower-potency agents, up to fourteen days for high potency), within two to four weeks of ultraviolet exposure, or in pregnancy and lactation where local practice prefers to postpone. Systemic immunosuppression also affects results.
4. Inform the patient about the purpose, the need to keep the area dry, and the practical precautions during testing, with written instructions where possible.

Patch testing should never delay treatment of an acute, generalised drug eruption, and patients with severe reactions need inpatient management rather than outpatient testing.^[5]

A biopsy is chosen for the question, not for the lesion alone. The main aim is to give the pathologist an adequate amount of tissue from the site most likely to yield a diagnosis while minimising disfigurement and preserving function.

• Incisional biopsy removes only a portion of a lesion and is the default when the lesion is large, when melanoma is not suspected, or when the question is a pattern diagnosis such as vasculitis, lupus or mucosal disease. It may be done by shave, scissor, curettage or punch technique.
• Excisional biopsy removes the entire visible lesion and is preferred for small lesions where complete removal is also therapeutic, and for any lesion where melanoma is suspected, so that accurate measurement and full assessment are possible.
• Shave biopsy samples the epidermis and superficial dermis with a blade and is useful for superficial or raised lesions; a deeper shave or scoop excision removes additional dermis.
• Punch biopsy removes a cylinder of skin and gives a full-thickness sample whose depth depends on punch size and operator technique; it is the standard for inflammatory dermatoses and for most non-neoplastic diagnoses.
• Forceps or scissor biopsy is used for skin tags and for small pedunculated lesions.

Practical points for selection:

• Biopsy the freshest, least altered lesion; avoid old, crusted or heavily excoriated areas in non-specific rashes.
• For blistering diseases, sample an early intact blister with some surrounding skin, and send a separate perilesional biopsy for direct immunofluorescence if available.
• Where a large lesion has several zones, include lesional, perilesional and, if possible, control skin, or sample the thickest or most indurated area.
• Suspected melanoma should be removed with adequate margins where possible and examined histologically rather than treated on clinical grounds alone.
• Haemostasis, suturing and wound care after biopsy are part of the procedure and should be explained in advance.

The classification into incisional and excisional, and the choice among shave, punch, scissor and excisional techniques, is based on site, depth and breadth of the necessary sample, as set out in the standard teaching on the procedure.^[3]

Record the examination findings in standard terms at the time. If a rash is being followed over time, use the same words at each visit and measure the same lesions. Photographs with a ruler are more useful than new descriptions. Tell the patient what warning signs require reassessment, and document the suspected diagnoses and the planned tests. After a biopsy, give written wound care instructions and a date for results review. After patch testing, record the allergens, concentrations and readings, and provide advice on avoidance in writing.

• Missing an area is the commonest single error in skin examination; the scalp, mucosa, genital skin and spaces between toes are where tumours and infections hide.
• Yellow or dim light makes erythema look brown and turns a warning sign into a harmless impression.
• Overusing "rash" as a diagnosis instead of describing the primary lesion and its distribution.
• Confusing primary with secondary changes: treating an excoriated rash without recognising that the primary lesion was a vesicle, or calling lichenified chronic eczema "psoriasis".
• Underestimating infiltration by never palpating.
• Assuming contact allergy from history alone, or misinterpreting irritant reactions during patch testing.
• Taking a biopsy from the wrong site or from a lesion that has already been treated.
• Bedside tests can be falsely negative if sampling is inadequate; repeat them rather than dismissing the diagnosis.

The American Academy of Dermatology guidance on rashes summarises features that need medical attention rather than observation:^[6]

• A rash over most of the body.
• A rash that blisters, becomes an open sore or leaves raw skin.
• Fever or illness accompanying the rash.
• A rash that spreads rapidly.
• A painful rash.
• A rash involving the eyes, lips, mouth or genital skin.

Emergency signs include trouble breathing or swallowing, or swelling of the eyes or lips, which require immediate care. Signs that infection has entered the skin include pus, yellow or golden crusts, swelling, warmth, an offensive smell, swollen lymph nodes or fever. If such features are present, treat and involve senior clinicians before any elective test.

The full examination costs nothing but time and good light. In settings without dermoscopy, a hand lens and daylight are adequate for most inflammatory disease; careful history and distribution analysis do more than equipment. Wood lamp is inexpensive and remains useful for fungus and pigment disorders. Potassium hydroxide preparation needs only a microscope and costs very little; nail clippings can be examined the same way without culture. Patch testing uses simple chambers and allergen preparations. If a biopsy cannot be processed locally, sending tissue in formalin to a regional laboratory, or performing a punch or shave sample with the simplest available instrument, is usually possible and better than no tissue diagnosis. Photographic records made with any available camera support remote review.

• Children: examine rapidly, in a warm room, and include the nappy area and scalp; systemic illness in children often shows in the skin first.
• Older adults: skin is thin and tears easily; minor purpura is common and may be unrelated to disease, but new lesions still require explanation.
• Pregnancy and lactation: stretch marks and vascular changes are normal; new severe itching, blistering or pigmentation may need investigation, and patch testing is often deferred.
• Dark skin: erythema is harder to see and may look purple or brown; palpation, surface change and distribution become more important.
• Immunocompromised patients: atypical infections, unusual distributions and drug eruptions are common; lower the threshold for biopsy and microbiological investigation.

• Examine the whole skin, including hair, nails and mucosa, in good light, in a fixed order.
• Describe every rash as primary lesion, secondary change, distribution and configuration, then palpation findings and evolution.
• Primary lesions reveal the disease process; do not let scratching and chronicity obscure them.
• Distribution terms such as flexural, extensor, dermatomal, acral, sun-exposed and symmetric are diagnostic clues in their own right.
• Palpation distinguishes flat from raised, solid from fluctuant and superficial from infiltrated disease.
• Dermoscopy extends the eye through magnification and controlled light, most importantly in pigmented lesions and keratinocyte cancers.
• Wood lamp examination requires a completely dark room and shows fluorescence in some infections and pigment disorders.
• Potassium hydroxide preparation of scale from the active edge is the standard screen for dermatophyte infection.
• Patch testing reproduces delayed hypersensitivity under occlusion and must be read up to seven days later.
• Choose an incisional or excisional biopsy, and a shave, punch or scissor technique, for the clinical question, the required depth and the pursuit of minimal scarring.
• Red flags such as generalised, blistering, painful, rapidly spreading or mucosal rashes, especially with fever, take priority over every test.

• Dermatology: contact dermatitis
• Dermatology: atopic eczema
• Dermatology: psoriasis
• Dermatology: fungal infections of skin and nails
• Dermatology: melanoma and skin cancer screening
• Dermatology: pigmented lesions and naevi

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