see also:

• dermatology

• the finding of linear skin lesions can often assist in the diagnosis of skin rashes as the list of differentials tends to be more limited.

• striae distensia

• skin becomes raised and inflamed with a localised wheal reaction when stroked, scratched, rubbed, and sometimes even slapped
• 4-5% of population have this familial skin disorder (also called dermatographism)
• see also urticaria

• many sources of contact dermatitis may be linear
• jellyfish stings
• Pederin toxin from crushing of certain beetles on the skin when brushing them away
  • Christmas eye disease is an incredibly painful monocular keratitis usually involving 90% of the epithelium (often punctate corneal ulcers becoming large geographic ulcers) affecting those in NE Victoria and SW NSW in summer as a result of exposure to the chemical pederin which is produced the crushing of certain types of small beetle in the eye when they crawl in there and are rubbed or blinked, or the toxin is rubbed into the eyes from your hands - usually of the genus Paederus (Staphylinidae, Rove beetles, up to 1cm, ant-like bettles with red abdomens) or genus Orthoperus (Corylophidae, minute hooded beetles which feed on fungi on bark). They can also cause severe linear dermatitis starting 12-36hrs after skin contact (prevent by washing ASAP with soap and water after suspected contact) and the so-called 'whiplash' stripe across the skin which may last up to 3 weeks. Pederin is a strong inhibitor of protein biosynthesis and it is a blistering agent. Generally occurs only between late October and early March. Most resolve with supportive care as per keratitis but some can scar. These may occur in localised outbreaks and may have been the cause of the biblical plague of boils.

• eating undercooked or raw shiitake mushrooms (Lentinula edodes) may cause pruritic flagellate erythema / shiitake dermatitis - a toxic or hypersensitivity reaction to lentinan which affects ~2% of people who eat them undercooked and presents a couple of days after ingestion ¹⁾
• bleomycin

• scabies particularly in digital web spaces has short linear lesions

• skin lesions occuring in lines of trauma
• linear external contact:
  • toxicodendron dermatitis (eg. poison ivy)
  • other contact dermatitis (eg. wrist bands, watches, rings, etc)
• direct inoculation of viral particles:
  • warts
  • molluscum contagiosum
• other conditions with linear lesions resulting from scratching
  • psoriasis
  • pityriasis rubra pilaris
  • lichen planus:
    • a chronic mucocutaneous disease that affects the skin, tongue, and oral mucosa.
    • the “5 Ps”: well-defined pruritic, planar, purple, polygonal papules
    • commonly affected sites are near the wrist and the ankle
    • tends to heal with prominent blue-black or brownish discoloration that persists for a long time
  • lichen nitidus
    • chronic rash characterized by 1-2 mm, discrete and uniform, shiny, flat-topped, pale flesh-colored or reddish-brown papules
    • usually affects children and young adults
    • linear pattern is common, especially on the forearms
  • vitiligo
    • depigmentation
  • lichen sclerosus
    • white patches on the skin, which may cause scarring
    • women 10x more affected than males. Mainly arises at menopause, and usually in the genital region
  • elastosis perforans serpiginosa
    • rare condition with serpiginous lesions
  • keratosis follicularis (Darier disease)
    • Darier's is a rare autosomal dominant condition characterized by dark crusty patches on the skin, sometimes containing pus
  • erythema elevatum diutinum
    • rare vasculitic condition thought to be paraneoplastic
• pathergy:
  • skin lesions following minor trauma
  • pyoderma gangrenosum
  • Behçet's disease

• capillary vasculitis processes
  • scarlet fever - Pastia's lines

• herpes zoster

• embryonal skin lines not usually visible but which may become evident in certain conditions forming V shape on the back, S swirls on anterior trunk and wavy lines on the scalp
• pigmentory disorders
• acquired skin rashes:
  • lichen striatus
  • lichen planus
  • lupus erythematosis
• genetic disorders

• livido reticularis
  • common in those with pronounced reaction to cool weather
  • is much less commonly is caused by underlying conditions such as cryoglobulinemia
• erythema ab igne
  • localized areas of reticulated erythema and hyperpigmentation due to chronic and repeated exposure to infrared radiation eg. laptops on bare thighs, heat packs, sitting near an open fire
• lichen planus in oral mucosa
• fifth disease (slapped check) usually develop lacy rash on inner aspect of upper arms

• creeping cutaneous larva migrans
• elastosis perforans serpiginosa
  • rare condition with serpiginous lesions

• tinea (ringworm)
• erythema multiforme - target lesions