Primary Skin Lesions

The identification and classification of skin lesions in a patient are important steps in the diagnosis of any skin disorder. Primary lesions represent the initial presentation of the disease process. Secondary lesions develop from irritated or manipulated primary lesions, and/or disease progression. Along with history, a comprehensive examination of the skin, appendages, and mucous membranes is required to differentiate between conditions. The key features noted during examination include the type, morphology, size, color, shape, arrangement, and distribution of the presenting lesions. At times, diagnostic procedures may be necessary.

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  • A flat, non-palpable skin lesion measuring ≤ 1 cm in size
  • Differs in color from surrounding skin (hypopigmented/hyperpigmented or erythematous)
  • Not raised or depressed compared to the skin surface
  • Examples: 
    • Freckles
    • Moles
    • Café-au-lait macules
    • Macules in rubella
    • Macules in measles
Hyperpigmented cafe-au-lait macules

Hyperpigmented café-au-lait macules in a patient with neurofibromatosis type 1

Image: “Breast cancer associated with neurofibromatosis type 1: A case series and review of the literature” by Khalil J, Afif M, Elkacemi H, Benoulaid M, Kebdani T, Benjaafar N. License: CC BY 4.0


  • A flat skin lesion measuring > 1 cm in size
  • Differs in color from the surrounding skin
  • Nonpalpable and larger than a macule
  • Examples include vitiligo and melasma.


  • A raised, palpable skin lesion measuring ≤ 1 cm in diameter
  • The color can indicate the diagnosis:
    • Brown or black papules are often melanocytic lesions.
    • Red papules are often vascular lesions.
  • Examples: 
    • Nevi
    • Warts
    • Lichen planus
    • Insect bites
    • Seborrheic keratoses
    • Molluscum contagiosum
    • Angiomas
    • Skin cancers


  • Raised skin lesion measuring > 1 cm in diameter
  • Usually have palpable surface change as lesion arises from the epidermis
  • May have a flat-topped or rounded appearance.
  • Examples:
    • Psoriasis
    • Granuloma annulare
    • Seborrheic dermatitis
    • Eczema
Severe plaque psoriasis

Severe plaque psoriasis

Image: “Psoriasis manum” by George Henry Fox. License: Public Domain


  • A large, firm lesion raised above the surface of the surrounding skin and measuring 1–5 cm
  • Usually extends into the dermis and subcutaneous tissue
  • The surface may be smooth, keratotic, ulcerated, or fungating.
  • Examples: 
    • Neurofibromas
    • Cysts
    • Lipomas


Image: “Breast cancer associated with neurofibromatosis type 1: A case series and review of the literature” by Khalil J, Afif M, Elkacemi H, Benoulaid M, Kebdani T, Benjaafar N. License: CC BY 4.0, cropped by Lecturio.


  • A small, fluid-containing blister (collection of fluid in the skin) measuring ≤ 1 cm in diameter
  • Raised above the plane of the surrounding skin
  • The fluid is visible as the lesions are translucent.
  • Observed in:
    • Chickenpox
    • Herpes zoster
    • Impetigo
    • Dermatitis herpetiformis
Vesicles from herpes simplex virus

Vesicles caused by herpes simplex virus

Image: “Transplant biology at a crossroads” by Sedwick C. License: CC BY 4.0, cropped by Lecturio.


  • A large, clear fluid-containing blister measuring > 1 cm in diameter
  • May be caused by:
    • Burns
    • Bites
    • Irritant/allergic contact dermatitis
    • Drug reactions
  • Classic autoimmune bullous diseases include pemphigus vulgaris and bullous pemphigoid.
Findings in bullous pemphigoid

Cutaneous findings in bullous pemphigoid:
Multiple large, tense vesicles and bullae in the groin on normal to mildly erythematous skin

Image: “Localized flexural bullous pemphigoid” by Mehta V., Balachandran C. License: CC BY 2.0

Urticaria (Wheals or Hives)

  • Sharply demarcated and elevated lesions with irregular borders:
    • Usually erythematous and may have central pallor
    • Formed due to sudden extravasation of fluid into the dermis
  • Wheals are pruritic and ALWAYS disappear within 24 hours.
  • Can be caused by:
    • Medication hypersensitivity
    • Insect stings or bites
    • Autoimmune conditions
  • Physical stimuli (e.g., temperature, pressure, sunlight)


Image: “Urticarial Vasculitis in a Teenage Girl” by McGuffin A, Vaughan A, Wolford J. License: CC BY 3.0


  • A vesicle filled with pus
  • Formed due to the collection of inflammatory exudate that is rich in leukocytes
  • May contain bacteria or may be sterile
  • Pustules are common in: 
    • Folliculitis
    • Pustular psoriasis
    • Scabies
    • Acne
Folliculitis example

Bacterial folliculitis on the lower leg presenting as follicular pustules

Image: “Folliculitis on lower leg” by Da pacem Domine. License: Public Domain


  • Also known as “spider veins
  • Appear as fine, bright red lines or a net-like pattern
  • Represent a dilation of capillaries that blanch upon pressure
  • Not elevated and are often found on the face, trunk, and around the nail bed
  • Telangiectasias occur in:
    • CREST (calcinosis, Raynaud’s phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia) syndrome
    • Dermatomyositis
    • Systemic sclerosis
    • Ataxia telangiectasia
    • Skin cancers
Nose telangiectasias

Nose telangiectasias:
a: Telangiectasias (arrows)
b: After treatment with cautery

Image: “Management of Facial Telangiectasias with Hand Cautery” by E Liapakis I, Englander M, Sinani R, I Paschalis E. License: CC BY 3.0


  • Punctate foci of hemorrhage (seen as small red, purple, or brown spots) measuring < 3 mm in size
  • Petechiae are seen in the setting of: 
    • Thrombocytopenia
    • Platelet dysfunction
    • Vasculitis
    • Infections (e.g., meningococcemia, Rocky Mountain spotted fever)
Petechiae around intravenous site

Petechiae around intravenous site

Image by Jeremy Greer, MD (Lecturio).


  • Extravasation of RBCs from cutaneous vessels in the skin and mucous membranes:
    • Usually palpable and non-blanching with diascopy
    • Usually red, purple, or even blue in color
  • Purpura is seen in leukocytoclastic vasculitis (e.g., Henoch-Schöenlein purpura and polyarteritis nodosa).
  • A large area of purpura may be called an ecchymosis.
Petechiae or purpura on the lower limb

Petechiae/purpura on the lower limb seen in Henoch-Schöenlein purpura

Image: “Henoch-Schönlein purpura in an older man presenting as rectal bleeding and IgA mesangioproliferative glomerulonephritis: A case report” by Cheungpasitporn W, Jirajariyavej T, Howarth CB, Rosen RM. License: CC BY 2.0

Approach to Diagnosing Skin Conditions

Complete medical history

  • Underlying conditions (e.g., autoimmune disorders, diabetes)
  • Accompanying symptoms (e.g., burning, itching)
  • Medications
  • Allergies
  • Evolution and duration of skin lesions, and aggravating and alleviating factors
  • Social, sexual, and travel history

Physical examination

A general physical examination as well as a focused dermatological examination should be performed:

  • Skin and its appendages as well as mucous membranes
  • Performed with the naked eye and using a dermatoscope

Skin features and commonly associated skin conditions and/or lesions to consider:

  • Texture: 
    • Raised: papule, plaque, nodule, cyst, wheal
    • Depressed: ulcer, atrophy
    • Flat: macule, patch
    • Fluid filled: vesicle, bulla, furuncle, pustule, and abscess
  • Morphology: 
    • Dome shaped: hemangioma
    • Flat topped: verruca plana
    • Umbilicated: molluscum contagiosum
    • Accuminate: condylomata acuminata
    • Verrucous: verruca vulgaris
    • Pedunculated: acrochordon (skin tag)
  • Diameter: varies depending on the condition
  • Composition: fluid-filled, pus-filled, blood-filled, or solid structures
  • Borders: regular or irregular, flat or raised
  • Color: hypopigmented, hyperpigmented, or erythema
  • Arrangement: grouped (herpetiform)/scattered
  • Configuration: 
    • Annular: tinea corporis, granuloma annulare
    • Round/discoid/nummular: eczema, discoid lupus
    • Polycyclic: urticaria
    • Arcuate: urticaria
    • Linear: scabies burrow, lichen nitidus
    • Reticular: livedo reticularis
    • Serpiginous: cutaneous larva migrans
    • Targetoid lesions: erythema multiforme
    • Whorled: incontinentia pigmenti
Primary skin lesions

Different primary skin lesions:
A macule is a flat ≤ 1 cm non-palpable skin lesion.
A papule is a raised ≤ 1 cm palpable skin lesion.
A nodule is a large 1–5 cm firm raised lesion, usually extending into the dermis and subcutaneous tissue.
A plaque is a raised > 1 cm skin lesion with palpable surface change as it arises from the epidermis.
A vesicle is a small ≤ 1 cm fluid-containing blister while a bulla is a large > 1 cm clear fluid-containing blister.

Image by Lecturio.

Diagnostic procedures

  • Skin biopsy (lesion excised, saucerized, or obtained by punch biopsy)
  • KOH preparation: 
    • Lesion scraped and placed on a glass microscope slide, where it is treated with 1 or 2 drops of 10%–20% KOH
    • If fungal infection suspected
  • Tzanck smear: cytologic technique when vesicular conditions are noted (herpes simplex or varicella zoster infections)
  • Diascopy: to determine if a lesion will blanch on pressure, differentiating a hemorrhagic (does not blanch) from a fluid-filled lesion
  • Wood’s light: 
    • Utilizes 360 nm UV light to evaluate lesions
    • Conditions: erythrasma (coral pink color), Pseudomonas wound infections (blue), vitiligo (white)
  • Patch test: allergens placed on patient’s back under occlusive dressings and checked for hypersensitivity reactions after 48 hours.


  1. Yancey, K.B., Lawley, T.J. (2018). Approach to the patient with a skin disorder. In Jameson, J., et al. (Eds.). Harrison’s Principles of Internal Medicine, 20e. McGraw-Hill.

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