Defining Skin Lesions
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Describing and defining skin lesions is a complicated business, and something that most doctors are not very good at!

There are a wide variety of terms used to describe skin lesions. In the days of smartphones, and quickly being able to send a picture to a colleague for assessment of a rash, this is perhaps less important than it used to be, but it is still useful to know some of the more common terms.

I find it helps to understand not only what the term describes, but the process that is giving rise to this type of rash, and I have summarised some of the terms below.


  • Flat
  • Often red (not always)
  • <1cm diameter
  • Well defined border
  • Arises from the epidermis

Macule and Patch

  • Raised and palpable lesion
  • <5mm diameter
  • Well defined border
  • Typically not compressible
  • Arises from the dermis

Papule and Plaque

  • A larger macula
  • Arises from the epidermis
  • Describes a combination of Macauley’s and Papuans
  • A papule >5mm diameter
  • Arises from he epidermis
  • A palpable lesion with a flat top
  • >1cm diameter
  • Well defined border
  • Not compressible
  • Raised
  • Blanches
  • Compressible
  • Caused by oedema of the dermis
  • A fluid filled lesion <5mm diameter
  • Raised
  • Arises from the epidermis

Vesicle and Bulla

  • A vesicles >5mm diameter
  • Visible collection of pus in the skin <10mm diameter
  • A pustule >10mm diameter
  • Bleeding into the dermis
  • Multiple dark coloured spots – can be red or purple in colour
  • Can be macular or papular
  • Purpura <2mm diameter
  • Swelling from a large bleed in the skin
  • Often tender and palpable
  • “Redness”
  • Increased vascularise – often due to an inflammatory process
  • Tiny white spots
  • Contain keratin, occurs as a result of blocked pilosebacious glands
  • Warty-like appearance
  • Tiny ‘finger-like’ projections from the skin surface
  • Typically from wart viruses (HPV viruses)
  • A deep skin defect
  • Goes all the way through the epidermis and may or may not effect the dermis

Erosion and Ulcer
Erosion and Ulcer
  • A shallow skin defect
  • Effects the epidermis only
  • A split in the skin
  • Effects dermis and epidermis
  • Scratch marks
  • Scar tissue that goes beyond the boundaries of the original injury

Types of rash

It may also help to try and split dermatological diagnoses into 7 types, as per Professor Robin Marks:

  • Infection
    • Bacterial
      • Impetigo
      • Cellulitis
    • Viral
      • Herpes simplex
      • Chicken pox
      • Warts
      • Pityriasis rosea
      • Viral rash – “viral exanthem”
    • Fungal
      • Tinea
      • Candidiasis
      • Pityriasis Versicolor
  • Acne
  • Psoriasis
  • Eczema
  • Urticaria
  • Sun-related skin cancers
  • Drug-related eruptions


Location and timing

  • Where is the rash?
  • When did it start?


  • Is it itchy?


  • Have you taken any medication recently?
  • [Has the appearance of the rash been changed by treatment?]


  • Does anybody you know have a similar rash?


  • Have you got a history of any rashes or anything similar?
  • Have you changed washing powder / soap / shower gel / skin products recently?
  • What do you do for work?


  • Murtagh‚Äôs General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
  • Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

Read more about our sources

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) currently works as a GP Registrar and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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