Rash. Rash history | by Aayush Pokharel | Oct, 2021

Aayush Pokharel

Much of the diagnosis comes from examining the rash or lesion itself, but history taking is still important.

Features of the rash:

  • Evolution of rash/lesion over time.
  • Onset at multiple sites and/or symmetrical? Suggests an internal cause.
  • Does sun exposure make it worse (e.g. SLE) or better (e.g. psoriasis)?

Associated symptoms:

  • Itch (common) and pain (uncommon), both of which can be explored with SOCRATES.
  • Ooze or weeping? Suggests eczema.
  • Loosing sleep from discomfort?

Possible causes:

  • Contact with substances at work or as part of a hobby. May cause allergic or irritant contact dermatitis.
  • Medications.

Sun exposure history if you suspect cancer:

  • Do you tan/burn often?
  • Sunbed use.
  • Lived abroad?
  • Worked outside?
  • Previous skin diseases.
  • Personal or family history of atopy, eczema, or psoriasis.
  • Any friends/family with an itchy rash? May suggest infectious cause such as scabies.
  • If problem is in the dermis, the skin stays smooth.
  • If in the epidermis, it won’t.

Crust (aka scab):

  • Orange-yellow bits of dry serum, pus, and/or blood.
  • Other lesions — rash, lump, ulcer — might lie underneath, so crust should be removed to check.

Scale (aka hyperkeratosis):

  • White-yellow flakes from a thickened stratum corneum (upper layer of epidermis) in which keratin has accumulated.
  • Most commonly seen in psoriasis.
  • May co-occur with crust.


  • Scale
  • Lichenification: thickened epidermis with exaggerated skin lines. Caused by constant scratching or rubbing.
  • Scarring: suggests damage to dermis. Can be hypertrophic — as in normal scarring or keloid scarring — or atrophic — post-acne or with steroid use.

Thinning/absences of skin layers:

  • Ulcer: full break (all the way through) of at least the epidermis. While healing it may feature exudate or crust (orange-yellow), pus (thick yellow), or necrotic tissue. Leave a scar.
  • Erosion: partial break, which heals without leaving a scar.
  • Excoriations: lots of small erosions which are self-inflicted from scratching.


  • Primary determinant of skin colour, from albino to black.
  • Eumelanin: appears dark brown if superficial, but blue if deep.
  • Phaeomelanin: gives a pink-red colour to skin, and red hair.


  • Pink, suggesting ↑O2.
  • Dusky purple, suggesting ↓O2. If it is non-blanching, this suggests capillary leak e.g. vasculitis, sepsis.


  • Green, yellow, and/or black.
  • This gunk is known as ‘slough’ (pronounced ‘sluff’).

Haemosiderin deposition:

  • Yellow-brown.
  • Causes: varicose eczema, haemochromatosis.


  • Rolled: BCC.
  • Well-demarcated: psoriasis.


  • Symmetry: internal/systemic cause.
  • Extensor/flexor.
  • Contact sensitivity e.g. on finger tips.
  • Sun-exposed.
  • Linear grouped papules: insect bites.
  • Mid-back spared: self-inflicted.

“On the { location }, there is a { widespread / localised / [a]symmetrical }, { erythematous / brown } { lesion / area / area of discrete lesion sites }, covering approximately { X x Y cm }. It is { well / poorly } demarcated, and contains { macules / papules / patches / nodules / pustules / vesicles / blisters }.”

6S + 3B:

  • Scabby
  • Scaly
  • Scrunched i.e. lichenification
  • Split: ulcer, erosion, excoriation
  • Scarred
  • Smooth: suggests a problem in the dermis as surface is unaffected.


  • Blood (including subcutaneously): erythematous, pink, purple.
  • Black: necrosis, may also be green and yellow.
  • Brown: melanin, haemosiderin.

The threshold between small and large lesions can be 5 mm (used below) or 1 cm.

  • Macule: small, flat, change in colour.
  • Patch: large (>5 mm), flat, change in colour.
  • Papule: small, raised lesion.
  • Nodule: large (>5 mm), raised lesion.
  • Plaque: flat-topped raised area, >5 mm, a broad or plateau-like nodule.
  • Vesicle:
  • Bulla: >5 mm
  • Blister: generic term for vesicles and bullae.
  • Pustule: pus-filled.
  • Cyst: cavity / closed sac, lined with epithelium, distinct from surrounding tissue. Semisolid (e.g. milia) or fluid-filled.

This is taken with the help of Medicos PDF app. You can download the app from Google Play Store for free.

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