Rashes History

Author – Kar Chang Natalie Ko  Editor Dr James Mackintosh

Last updated 31/01/24

Table of Contents


Rashes are a common presenting complaint in primary care. While examination forms a larger part of the assessment than in many other presentations, taking a good history is still an important differentiator between diagnoses.  

Presenting Complaint


Acral distribution (extremities such as hands, feet, fingers)

e.g. hand, foot and mouth disease

Extensor distribution (areas where joints extent such as knees, elbows, knuckles)

e.g. psoriasis

Flexural distribution (areas where joints bends such as inner aspects of elbows)

e.g. eczema

Follicular distribution (areas involving hair follicles)

e.g. acne, folliculitis

Dermatomal distribution (areas of skin supplied by a specific branch of a nerve)

e.g. shingles

Seborrhoeic distribution (areas rich in sebaceous glands)

e.g. seborrhoeic dermatitis


Early childhood/ adolescence

e.g. molluscum contagiosum, impetigo, acne vulgaris, eczema

Late adulthood

e.g. Rosacea (ages of 30-50), shingles (age of 50 or over)



– Confluent (merging lesions) e.g. urticaria

– Target (concentric rings with a bull’s eye pattern) e.g. erythema multiforme

– Annular (ring-like lesions) e.g. tinea corporis



– Purpuric ( reddish/ purple discolouration) e.g. vasculitis

– Hypopigmented (areas of paler skin) e.g. vitiligo, pityriasis versicolour



– Papule ( solid raised palpable lesion less than 0.5cm in diameter) e.g. molluscum contagiosum

– Pustule (pus-containing lesion less than 0.5cm in diameter) e.g. rosacea

– Plaque (palpable flat lesion greater than 1 cm in diameter) e.g. psoriasis, lichen planus


Secondary lesions

– Scales e.g. psoriasis, pityriasis rosea

– Lichenification (thickening of epidermis with exaggeration of normal skin lines) e.g. chronic eczema, lichen planus


Dermatomal spread e.g. shingles

Areas disturbed by allergen e.g. contact dermatitis

Facial area to trunk and limbs e.g. erythema infectiosum

Single oval lesion to smaller widespread scaley lesions e.g. pityriasis rosea

Associated Symptoms

Fever e.g. measles, scarlet fever, Lyme disease

Itching e.g. hives, eczema, allergic reaction, insect bites

Scaling/ flaking e.g. psoriasis, seborrhoeic dermatitis

Exacerbating Factors

Irritants and allergens e.g. contact dermatitis, allergic reactions

Heating and sweating e.g. heat rash, miliaria

Stress e.g. eczema, psoriasis

Significant pain e.g. cellulitis, shingles


Acute e.g. cellulitis, shingles, scarlet fever, contact dermatitis, drug reaction

Relapsing remitting e.g. eczema, urticaria

Chronic e.g. venous insufficiency, seborrheic dermatitis, psoriasis


Considerable overlap exists among various causes of rashes. The table below provides a concise summary of the key characteristics of common differential diagnoses.

Differential Features
Itching at flexural creases with erythematous dry and itchy lesions that are poorly demarcated.
Superficial, skin-coloured or pale swellings surrounded by redness, lasting anywhere from a few minutes to 24 hours, and sometimes occurring alongside angioedema, which involves deeper swelling in the skin or mucous membranes.
Pityriasis versicolour
Hypopigmented patches that usually appear on the chest or back. Often noticed following holiday in the sun.
Well-demarcated area of erythema on skin with warmth and tenderness. Can be associated with fevers. Usually following skin break such as an insect bite.
Purpuric rash ranges in size, purpuric non-blanching rash Symptoms suggesting higher severity: haematuria, chest pain, abdominal pain, meningococcal sepsis.
Necrotising fasciitis
Pain and tenderness out of proportion to what is seen on physical examination.
Chronic venous insufficiency
Hyperpigmentation, venous ulcers, dermatitis +/-pain and itching of skin on the ankles and shins bilaterally.
Necrotising Enterocolitis (3-12 days after birth)
Generally unwell, intolerance to feeds, bilious vomit, bloody stools, distended/ tender abdomen
Cold sores / genital herpes
Blistering lesions intensely painful, genital: urinary symptoms.
Steven-JohnsonSyndrome (SJS) / ToxicEpidermal Necrolysis(TEN)
SJS: less than 10% of body surface area TEN: affects more than 10% Starts with non-specific symptoms which later develops into a purple or erythematous rash that spreads across the skin with blistering and shedding. Possible involvement of mucosal membranes. Nikolsky's sign
Pityriasis Rosea
A large circular herald patch which later develops into small erythematous oval scaly patches producing a “fir-tree appearance”
Flushing and telangiectasia, persistent erythema with papules and pustules affecting nose, cheeks and forehead, exacerbated by sunlight.
Erythematous, macular rash that quickly becomes vesicular affecting specific dermatomes (commonly T1-L2) with severe burning pain.
- Plaque psoriasis: well-demarcated red, scaly patches affecting extensor surfaces, sacrum and scalp - Guttate psoriasis: Multiple red, teardrop lesions appear on the body, triggered by a streptococcal infection.

Red Flags

It is crucial to show that you are taking into account the possibility of severe causes of rashes by asking pertinent red flag questions to assess them.

Non-blanching petechial rash – meningococcal septicaemia 

Severe pain out of proportion to rash – necrotising fasciitis 

Skin sloughing off – Steven Johnson Syndrome

Systemic symptoms such as fever, lethargy and infective symptoms that may indicate sepsis.


When conducting a patient history, it is necessary to inquire about relevant symptoms in other body parts, travel history, past medical history, medications & immunisations, allergies, family history and social history. In the case of an acute rash history, you can showcase your knowledge of different causes by explicitly probing into the following aspects:

Past Medical History

Diabetes – acanthosis nigricans

Inflammatory bowel disease – pyoderma gangrenosum, erythema nodosum

Coeliac disease – dermatitis herpetiformis

Travel History

Erythema migrans after visiting a location with potential tick exposure.

Sun exposure can worsen systemic lupus erythematous but improves psoriasis.

Family History

Family history of asthma, atopy, allergies are often associated with eczema.

Does anyone in the family have a similar rash? (e.g. scabies)


Social History

Diet: diet with gluten can trigger rash associated with coeliac disease

IVDU increases risk of cellulitis and necrotising at injection sites

Occupation: Are there any occupational exposures such as soaps, frequent handwashing, chemicals?

Exposures: Has the patient switched soaps, laundry detergent or cleaning products recently?


During the examination of a patient, it is crucial to keep in mind the potential diagnoses and carefully observe for signs that either support or contradict them. When evaluating a patient with a rash, it is necessary to conduct a thorough assessment that includes general inspection (taking note of the number, location, and distribution of the skin abnormalities), close inspection (examining both the surface and deeper characteristics), palpation, and systemic examination (examining the nails, hands, elbows, hair, scalp, and oral mucosa) as a minimum requirement. Certain skin conditions may present with manifestations beyond the skin, while other skin lesions can be a result of an underlying systemic disease process. Therefore, performing a comprehensive assessment is essential to identify any relevant pathology.

  1.  Patient Info, Dermatological History and Examination- https://patient.info/doctor/dermatological-history-and-examination
  2. Primary Care Dermatology Society, Taking a Dermatology History – https://www.pcds.org.uk/skin-disease-history
  3. DermNet – dermnetnz.org/image-library

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