Clinical Presentation: Erythematous, excoriated eczematous plaque in the antecubital fossa (elbow crease) with skin dryness.
Source: Wikimedia Commons / Creative Commons
Key Hallmark
Intense itch ("the itch that rashes") with a classic flexural distribution in older children and adults (elbow creases, behind knees, wrists, neck), and extensor/facial distribution in infants.
What Happens in the Skin?
Deficiency in skin barrier proteins (e.g. filaggrin) allows moisture to escape and environmental irritants to penetrate, triggering persistent immune-mediated inflammation.
Key Visual Features
- Dry, scaly, reddened skin (erythema)
- Small bumps (papules) that weep when scratched
- Lichenification (thickened, leathery skin lines) in chronic cases
Typical Sites:
Clinical Presentation: Well-demarcated erythematous reaction showing sharp boundaries matching the exact area of contact with adhesive tape.
Source: Wikimedia Commons / Creative Commons
Key Hallmark
Sharp geometric or localized demarcation corresponding precisely to where the offending substance touched the skin (e.g. watch strap, belt buckle nickel, bandaid adhesive, perfume, plants).
Irritant vs. Allergic
Irritant (80%): Immediate or gradual chemical damage from soaps, detergents, solvents, or frequent wet work. Anyone can get it.
Allergic (20%): Delayed immune hypersensitivity (24-72h post-exposure) to nickel, fragrances, preservatives, or plants (poison ivy/oak).
Allergic (20%): Delayed immune hypersensitivity (24-72h post-exposure) to nickel, fragrances, preservatives, or plants (poison ivy/oak).
Key Visual Features
- Well-defined, geometric borders matching exposure
- Acute blistering (vesicles), weeping, and swelling
- Burning/stinging often prominent in irritant forms
- Severe localized itch prominent in allergic forms
Typical Sites:
Clinical Presentation: Greasy, yellowish scales over salmon-pink patches along the nasolabial folds, eyebrow margins, and hair-bearing scalp.
Source: Wikimedia Commons / Creative Commons
Key Hallmark
Greasy, yellowish, bran-like scales overlying salmon-pink patches restricted to sebum-rich areas (scalp, eyebrows, nasolabial folds, retroauricular folds, and central chest).
Underlying Cause
Not a contagious infection, but an inflammatory reaction to the breakdown products of skin sebum by normal resident Malassezia yeasts on the skin surface.
Key Visual Features
- Oily/greasy yellow-white flakes and scales
- Pinkish or dull red background erythema
- Mild or intermittent itch (less intense than atopic eczema)
- Thick adherent crusting on infant scalp ("cradle cap")
Typical Sites:
Clinical Presentation: Small, deep-seated 1-2 mm tense vesicles resembling "tapioca pearls" along the lateral border of the finger.
Source: Wikimedia Commons / Maslesha / CC BY-SA 3.0
Key Hallmark
"Tapioca pudding" appearance: Crops of intensely itchy, deep-seated, clear fluid-filled vesicles (blisters) exclusively along the sides of fingers, palms of hands, and soles of feet.
Natural Course
Erupts acutely with burning or intense pricking itch. Over 2-3 weeks, vesicles dry out, leaving desquamation (peeling), fissures, and painful cracked skin.
Key Visual Features
- Small (1–2 mm), tense, deeply embedded blisters
- Vesicles can coalesce into larger bullae
- Pruritus precedes the visual eruption
- Late-stage hand peeling and painful linear cracks
Typical Sites:
Clinical Presentation: Discrete, coin-shaped (discoid) crusted erythematous plaque with papules and tiny vesicles on the outer limb.
Source: Wikimedia Commons / Creative Commons
Key Hallmark
Discrete, coin-shaped (circular or oval) plaques (1–5 cm) that lack central clearing — helping distinguish it from ringworm (tinea corporis).
Clinical Behavior
Starts as tiny clusters of itchy papules and vesicles that quickly coalesce into discrete circular discs. Often highly stubborn and prone to secondary bacterial crusting.
Key Visual Features
- Well-circumscribed round discs without central clearing
- Acute phase: oozy, vesicular, crusted surface
- Chronic phase: dry, scaly, lichenified coin plaques
- Prominent moderate-to-severe itching
Typical Sites:
Clinical Presentation: Lower leg erythema, pitting oedema, and characteristic reddish-brown hemosiderin staining above the medial malleolus.
Source: Wikimedia Commons / Creative Commons
Key Hallmark
Rusty brown or cayenne-pepper pigmentation (hemosiderin staining) on the lower legs and ankles, associated with pitting oedema and varicose changes.
Underlying Mechanism
Incompetent venous valves cause blood pooling (stasis). High hydrostatic pressure forces red blood cells into tissue; breakdown of haemoglobin deposits iron (hemosiderin).
Key Visual Features
- Rusty, mottled brownish-bronze skin discolouration
- Oedema (leg swelling, worse after standing all day)
- Dryness, scaling, dilated venules, and fragile skin
- Risk of lipodermatosclerosis ("inverted champagne bottle")
Typical Sites:
Clinical Presentation: Clustered micro-papules and pustules around the mouth with characteristic clear sparing of the skin directly bordering the lips.
Source: Wikimedia Commons / Creative Commons
Key Hallmark
Clear margin around the lips (sparing of the vermilion border): Clusters of tiny 1–2 mm pink bumps/pustules around mouth, chin, and nasolabial folds with a distinct pale, clear border hugging the lip edge.
Triggers & Pitfalls
Frequently provoked or worsened by topical steroid creams (which cause initial improvement followed by severe rebound flaring), rich facial moisturisers, fluorinated toothpaste, or sunscreen.
Key Visual Features
- Clusters of tiny, discrete pink-red papules and small pustules
- Clear 2–4 mm zone of normal skin around the lip border
- Burning, stinging, or skin tightness (itch is often minimal)
- Can extend around eyes (periocular) and nose (perinasal)
Typical Sites:
Clinical Presentation: Chronic, circumscribed hyperkeratotic plaque with marked lichenification on the anterior lower leg (shin).
Source: Wikimedia Commons / Eyon / CC BY-SA 3.0
Key Hallmark
Leathery, heavily thickened plaques (lichenification) with prominently accentuated criss-cross skin markings, precisely localized to easily reachable body sites.
The Itch-Scratch Reflex
Mechanical trauma from repetitive scratching stimulates epidermal hyperplasia and nerve proliferation in the skin, making the lesion even itchier and more habitual (often subconscious during sleep or stress).
Key Visual Features
- Thick, leathery, palpable plaque with prominent skin lines
- Hyperpigmentation (darkened / brownish-grey hue)
- Surrounding excoriations (linear scratch marks)
- Well-circumscribed, solitary or few discrete plaques
Typical Sites: