localised rashes

see also:

• facial rashes
• the linear skin lesion or rash
• paediatric exanthems
• acute rashes in adults

• physical trauma - bruises, etc
• thermal burns
• chemical caustic burns - acids, alkalis, skin irritants
• radiation burns
• prolonged exposure to a direct heat source giving the classical reticular “rash” of erythema ab igne
• insect or spider bite - usually a central vesicle with surrounding wheal
• localised infection:
  • impetigo
  • cellulitis
  • erysipelas
  • abscess
  • herpetic whitlow
  • fungal infection
  • dermatomal - herpes zoster (shingles)
  • molluscum contagiosum
  • tinea corporis
  • tinea pedis
  • tinea cruris
  • orf in sheep farmers
  • syphilis - primary chancre

• exposure to UV radiation / sun:
  • see also: https://dermnetnz.org/topics/photosensitivity
  • sunburn
  • photosensitivity reaction to medications, etc
    • phototoxic reaction (exaggerated sunburn without any immune response)
    • photoallergic reaction (eczematous photodermatitis associated with a delayed immune hypersensivity response)
    • common medications:
      • thiazides, tetracyclines, non-steroidal anti-inflammatory drugs (NSAIDs), phenothiazines, voriconazole, quinine, vemurafenib
    • common phototoxic chemicals:
      • psoralens in plants, vegetables, fruit; fragrances in cosmetics; sunscreen chemicals; dyes and disinfectants
      • pseudoporphyria: induced by drugs and/or renal insufficiency.
  • photoexacerbated condition describes a flare of an underlying skin disease on exposure to sunlight
    • cutaneous lupus
    • systemic lupus erythematosus (SLE)
    • dermatomyositis
    • Darier disease
    • acne rosacea
    • pemphigus vulgaris
    • pemphigus foliaceus
    • atopic dermatitis
    • psoriasis
  • primary or idiopathic photodermatoses:
    • polymorphic light eruption
    • Juvenile spring eruption
    • rare conditions:
      • actinic folliculitis
      • actinic prurigo
      • solar urticaria
      • chronic actinic/photosensitivity dermatitis
      • hydroa vacciniforme (associated with EBV / glandular fever / infectious mononucleosis)
  • metabolic photodermatoses:
    • porphyria cutanea tarda
    • erythropoeitic protoporphyria
    • variegate porphyria
    • erythropoeitic porphyria (Gunther disease)
    • pellagra (initial photosensitivity)
  • rarely, genetic photodermatoses:
    • xeroderma pigmentosum, Bloom syndrome, Rothmund-Thomson syndrome, Cockayne syndrome, Hartnup disease
• exposure to cold:
  • chilblains
  • frostbite
• other causes of exposure-related rashes:
  • acne vulgaris due to follicular occlusion by sebum and keratin
  • contact or irritant dermatitis due to makeup and suntan lotions, industrial chemicals, etc
  • airborne contact dermatitis due to plant pollens, such as sesquiterpene lactone.
  • mosquito bites
  • biting midge / “sand fly” bites - very itchy, red papulovesicular lesions 12-24hrs after bites - often mainly on legs if exposed.
  • papular urticaria
• in addition, there are some relatively specific conditions related to the face primarily:
  • see facial rashes

• exposure to warm conditions:
  • prickly heat rash
  • fungal infections eg. tinea cruris, pityriasis versicolor
• exposure to inadequately warm clothes in very cold weather:
  • chilblains
  • frostbite
• exposure to chemicals in the clothing
  • contact dermatitis eg. rubber gloves
  • caustic or irritant dermatitis eg. inadequately washed clothes, contaminated clothing
• NB. many of the exanthems only involve trunk and limbs sparing face, palms - see acute rashes in adults

• see the linear skin lesion or rash

• see facial rashes

• pityriasis rosea
• pityriasis versicolor but may involve neck/arms, yellow-green flourescent on Wood's lamp
• Grover's disease (transient acantholytic dermatosis) - common in middle age
• scabies - also usually hands
• herpes zoster (shingles)

• tinea cruris
• heat rash / miliaria rubra
• herpes zoster (shingles)
• primary syphilis chancre
• Herpes simplex virus (HSV)
• candida fungal infection / thrush
• contact dermatitis eg. to rubber condoms

• cellulitis
• folliculitis
• tinea corporis
• nodules on shins suggest erythema nodosum
• venous dermatosis from venous insufficiency
• varicose dermatitis overlying varicosities
• gravitational dermatitis
• capillaritis
• pretibial pruritic papular dermatitis
• prurigo nodularis
• pretibial myxoedema
• lichen simplex from scratching, rubbing, etc
• contact dermatitis
• psoriasis (knees mainly)
• lichen planus
• superficial basal cell carcinomas
• necrobiosis lipoidica
• panniculitis
• vasculitis
• asteatotic eczema “crackled dry skin” most commonly affects the shins and is common in the elderly
• biting midges / “sand fly” bites often predominantly affect lower legs

• see also the painful foot
• corns
• pressure blisters
• foreign body reactions to embedded objects
• cellulitis
• diabetic foot ulcers
• arterial insufficiency
  • arterial ulcers
• plantar warts
• cracked heels
• tinea pedis
• pitted keratolysis
  • associated with Kytococcus sedentarius and foul foot odour from sweaty feet
• contact dermatitis
  • eg. rubber in shoes, chemical contact
• lichen planus (esp. ankles)

• hand, foot and mouth disease (mainly children, causes purplish blisters as well as fevers, malaise)
• juvenile palmar-plantar dermatosis “sweaty-sock syndrome” (mainly toddlers, school-aged children)
• atopic dermatitis (may cause chronic hand and foot dermatitis)
• secondary syphilis (multiple red lesions on palms and soles)
• erythema multiforme (may present as target lesions mainly on palms)
• gononoccoccal (rarely can cause small, painful, red spots or pustules mainly of palms and soles)
• palmoplantar pustulosis (PPP) / pustular psoriasis (rare, recurrent/chronic red scaly / pustular rash)
• contact dermatitis
• dyshidrotic eczema (causing small, itchy blisters)
• hand-foot syndrome (a chemotherapy side effect causing redness and swelling)
• tinea pedia / tinea mannuum
• acute cutaneous lupus erythematosus
• adult-onset Still's disease
• palmar erythema / plantar erythema (non-painful red warm skin mainly proximal palms and heels)

• see also: the linear skin lesion or rash
• fungal infections
• ulcers:
  • Buruli ulcer / Bairnsdale ulcer
  • venous leg ulcers
  • arterial / diabetic foot ulcers
  • pyoderma gangrenosum - starts like an insect bite, usually very painful, develop a purple undermined edge
• atopic eczema / dermatitis - usually mainly on flexure surfaces
• psoriasis - usually mainly on extensor surfaces
• contact dermatitis with repeated exposure
• chronic urticarias
• lichen simplex - repeated injury eg. scratching
• lichen planus - esp. wrists, ankles
• lupus
• plus there are many other chronic dermatoses