What is a rash?

RashesA rash is defined as a change in the skin’s appearance, which may involve alternations in texture (eg rough or smooth) and/or colour. The skin may also become itchy, warmer, dry, cracked, blistered, lumpy or painful. Depending on where the rash is located, other symptoms you are experiencing, what you have been exposed to and any family history, there are many causes for a rash.
It is therefore very important to be aware of where the rash initially arises from, how it changes or spreads and recognize symptoms and signs that suggest that you should seek medical attention immediately. These details and other important issues such as common causes, associated medical conditions and basic management of rashes will be discussed below.
Rashes can be divided into acute (short term) and chronic (longer term) causes. Within the acute group, they can be blanching (disappearing when pressed) or non-blanching. In the chronic group, it is useful to divide them into itchy and non-itchy causes. There are also a number of medical conditions which can be associated with rashes.

Common causes of rashes

There are many causes of rashes. It is useful to divide the common causes into two groups: those that develop quickly (acute) vs those that have been present for a longer period of time (chronic).

Acute skin rashes

Blanching rash (rash disappears when pressed)

Viral infections

Skin rashes seen depend on the virus involved.
In chicken pox, the varicella zoster virus produces groups of many vesicles, each like a drop of water on a reddened base on the trunk, face, extremities and inside of the mouth.
The measles virus produces a rash with flattened and raised areas, starting on the face and progressing to involve the trunk and limbs. White spots like salt grains on a red base inside the mouth (Koplik’s spots) are characteristic of measles.
Herpes zoster virus can cause crusting infection with fluid filled collections, affecting areas such as the lips.

Bacterial infections (impetigo)

Bacteria from groups called Staphylococcal and Streptococcal species are most commonly implicated in skin infections. You may develop a skin infection due to a wound in the skin, which has broken the barrier to preventing external organisms from entering the body.
With bacterial infections, commonly:

  • skin is red,
  • crusting skin
  • scaling skin
  • blistering skin and
  • pus producing skin.

Acute skin allergy reactions

  • Urticaria: Urticaria is an allergic reaction in the skin seen as a well circumscribed area of swelling, which usually lasts hours or days. You may feel extremely itchy, and these areas of swelling can be pink or skin coloured.
  • Insect bite-caused rashes: Mosquitoes, spiders and other insects can bite any part of the body. Bites are usually raised lumps that become red and extremely itchy. Flea bites usually occur around the ankles, possibly progressing onto fluid filled collections.
  • Vasculitis: Skin changes due to vasculitis are largely determined by the size and site of affected vessels. In a condition called hypersensitivity vasculitis, there are usually many red / purple skin lesions, predominantly located on the legs.
  • Atopic dermatitis / allergic contact dermatitis: Dermatitis is a pattern of inflammation in the skin, which may follow contact with an external skin irritating substance or which may develop without any apparent external cause. The term eczema is commonly used to refer to the latter condition. We tend to see this skin condition in people with allergies or asthma. The rash is generally red, itchy, and scaly.
  • Drugs: The range of skin lesions produced by drugs are countless, but in most cases, presents with widespread bodily involvement.

Non-blanching rash (rash doesn’t disappear when pressed)

Meningococcal disease

Meningococcal disease classically presents as a red / purple skin rash in an ill patient. The rash may progress to join together over certain parts of the body, with extensive purple bruising. Sometimes, there may be a raised, palpable rash that disappears when pressed (blanching). Usually the patient is very unwell, out of proportion to the viral illness.

Chronic rashes

Pruritic (itchy)

  • Atopic dermatitis
  • Scabies: This is caused by the mite Sarcoptes scabiei and is acquired by close physical contact with someone suffering from the disease. Scabies symptoms include intense itching, burrows and the scabies rash. Burrows are found principally in the hands and feet – between the fingers, toes and wrists. Each burrow is several millimeters long, light brown in colour and often surrounded by skin redness. The scabies rash looks like many tiny papules (elevations of the skin) grouped around the axillary folds (ie armpit, neck), umbilicus and the thighs.
  • Ringworm: Symptoms of ringworm (Tinea Corporis):
    • Characteristic skin lesions are located all over the body
    • Large, red and scaly.

Non pruritic (not itchy)

  • Psoriasis: Classically, psoriasis tends to occur as red, scaly itchy patches of skin with a silvery white scale over the joints and scalp areas.
  • Seborrhoeic dermatitis: Seborrhoeic dermatitis is a skin rash that can appear in patches on the scalp, face, chest, upper back and in the skin folds in the joint areas. Scalp involvement can present as itchy, red, widespread scaling. Involvement of the scalp is called dandruff in adults and cradle cap in infants.
  • Warts: Common warts coming in many different sizes and shapes. Warts can be single or multiple raised, cauliflower like lesions which occur most frequently on the hands. Plantar warts (ie located on the feet) usually appear as small areas of thickened skin.
  • Molluscum contagiosum: Pink /flesh coloured papules with a smooth surface and small central depressed / thickened area, scattered all over the body are found.
  • Cancers: Superficial basal cell carcinomas of the skin can present as slowly enlarging, red scaling skin areas. Bowen’s disease refers to squamous cell carcinomas that are still confined to their primary location. These look like slowly enlarging, red scaly patches with a well defined border on sun exposed and sun protected areas.

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Medical conditions associated with a skin rash

RashesSkin rashes can be an indication of disease processes occurring in the body.

Erythema nodosum

Erythema nodosum is a skin condition where red, tender/painful lumps form on the shins, and less commonly the thighs and forearms. More commonly occurring in young females, the condition can be caused by many factors, including; bacterial infection, drugs (oral contraceptive pill, aspirin), or inflammatory bowel disease

Erythema multiforme

This skin rash usually appears suddenly, after exposure to the causative agent. Although the cause is unknown in about 50%, possible causes include: herpes simplex virus, other viral infections, drugs (anti-epileptic drugs), connective tissue diseases (systemic lupus erythematosus) and HIV infection.

Acanthosis nigricans

Acanthosis nigricans presents as darkened areas of thick skin, especially in the skin folds around the flexural areas (armpits, neck, groin). These changes are often seen in overweight patients who have a high level of insulin.


Dermatomyositis is inflamed skin and muscle which may occur in childhood or adult life. It usually presents with distinctive facial redness, a purple coloured skin rash around the eyes, and swelling. The knuckles and arms and legs may develop blue/red nodules or patches. If you are affected by dermatomyositis you may feel some muscle discomfort and weakness.


Scleroderma refers to a group of diseases in which there are changes in the layers of the skin, producing thickened layers, and destruction of hair follicles and sweat glands. The lungs, bowels, kidneys and heart may all be affected. Skin may become tight and tethered, especially around the hands, mouth and nose.

Lupus erythematosus

The two main forms of lupus erythematosus include:

  • Discoid: In this condition, disease is limited to the skin, classically affecting light exposed areas. The lesions are well defined, consisting of scaling skin and areas of reddened skin. Changes are predominantly located on the cheeks, forehead and nose.
  • Systemic: In the systemic form of lupus, skin lesions are associated with multi organ involvement, including the kidneys, heart, lungs, brain and joints. This form is much more common in women and can lead a short, severe, course of disease or be a more progressive process. Classically there is facial redness in a butterfly distribution (involving the cheeks linked by a band of redness across the nose).


The most common skin changes in sarcoidosis include:

  • Orange-brown papules, nodules and patches;
  • Tender red nodules on the legs (erythema nodosum);
  • Dusky red lesions on the nose and fingers (lupus pernio).

Diabetes mellitus

Diabetes mellitus can be associated with many skin changes. These include: symptoms of fungal and bacterial infections and disease affecting the arteries in the body. Skin changes specific to diabetes include: necrobiosis lipoidica (an area of redness typically located over the shins, yellow in colour and with a depressed center with or without ulcers. Diabetic dermopathy is seen as red-brown flat topped papules.

Systemic malignant disease

Particular skin rashes may be a manifestation of underlying malignancies. Rarely, tumours may spread to the skin where they can present as collections of pus or palpable lumps which may continue to develop into ulceration of the skin.



When you visit the health practitioner, he or she may ask you some of the following information about your skin rash:

  • Rash characteristics:
    • Time course of skin rash (how your rash started, how rash has progressed, changes over time),
    • Distribution of skin lesions
    • Types of lesion (skin redness, skin scaling, thickening of skin, cracks in skin)
    • Changes in skin colour
    • Associated symptoms (skin dryness, itching skin, scratching)
    • Any previous episodes
  • Past medical history:
  • Family history:
    • Allergic diseases (asthma, hayfever, rhinitis)
    • Psoriasis
    • Itchy lesions / scabies
  • Drug / allergy history:
    • Have you taken any new drugs recently?
    • What medications are you currently on?
  • Aggravating factors:
    • Do any of the following make the rash worse?
      • Sunlight exposure
      • Diet
      • Woolen clothes
      • Foods
      • Animals
    • Have you been in contact with anyone else with a similar rash?
    • Is this the first time you’ve had the skin rash? If not, how was it treated last time?
  • Social history:
    • How is this skin rash affecting your life – school, work, sleep. Do you or anyone else in your household smoke?
    • Do you have any pets?

Skin examination

When the doctor/dermatologist examines you, he or she may find the following signs by looking at the skin rash and also feeling the surface of the skin where required.
Looking at the rash, the doctor can determine whether the lesion involves the external layer of the skin (the dermis) or the deeper layers (the epidermis). With rashes that extend deeper into the skin, there may be changes such as scaling skin, crusting skin, weeping and / or formation of vesicles (small collections of fluid). If there are changes in the deeper layers of the skin, the superficial layers are usually also affected. There may be lumps, papules (elevations of the skin) and / or nodules. By feeling the skin during examination, the doctor can get a good idea of the texture / consistency of the skin rash.
Looking at where the rash is distributed, the doctor can also get an idea of what may be causing the skin rash. Therefore it is very important to tell your doctor about all the places on your body that are affected by rashes.
In some skin rash cases, the dermatologist may need to do a more thorough examination of the body, looking at parts such as the nails, mouth and scalp.

Medical warning signs

You should seek medical help if:

  • You find it difficult to breathe, your throat is tight, or your face becomes swollen.
  • Your skin rash symptoms and any associated symptoms become worse / persist.
  • You have any signs of infection such as areas of intense redness, swelling, pain, pus or discharge.
  • You have recently started on new medications.
  • Your child has a purple rash that looks like bruising, especially if accompanied by symptoms such as altered conscious level, increased irritability, fever and altered cry.


  1. Buxton P. ABC of Dermatology. London: BMJ Publishing Group Pty Ltd; 2005.
  2. Kumar P, Clark M. Clinical Medicine. United Kingdom: WB Saunders; 2002.
  3. Lissauer T, Clayden G. Illustrated Textbook of Paediatrics. Spain; Mosby International Limited, 2003.
  4. Murtagh J. General Practice; Skin Conditions. Australia: McGraw-Hill Australia Pty Ltd; 2003
  5. Rotstein H. Principles and Practice of Dermatology. Australia: Reed International Books Australia Pty Ltd; 1998
  6. White G. Colour Atlas of Dermatology. Spain: Elsevier Limited; 2004.

Diseases presenting with skin rashes include:

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