Red flag symptoms
- Rash covering more than 90% of a person’s body surface area
- Punched-out lesions in a person with eczema
- An unwell patient (adult or child)
- Nausea and vomiting
- Non-blanching rash
- Arthralgia and muscle pains
- Blisters and bullae
- Scalded skin appearance
- Skin lesions
Skin rashes are a very common reason for people to present to general practice. Often, they will present early and in an undifferentiated way making them difficult to diagnose.
They can be a sign of many different pathologies and a good history is important. Patients can find rashes very irritating and will sometimes be worried about them being infectious. They may also worry about the cosmetic appearance. Some may have already been to a chemist and tried various over-the-counter products.
A history of a skin rash should include the duration it has been present, and whether it is itchy, sore, tingly or scabbing. Associated symptoms like fever, cough, sore throat, joint pain and general health are important.
In children with rashes, ask about nausea and vomiting, headaches, photophobia and whether the rash is blanching.
When examining a rash, it is important to expose the patient to be able to look at the extent of the rash, whilst maintaining the patient’s dignity as much as possible. Consideration should be given to the colour, size, appearance and texture, shape, distribution and progression over time of the rash.
The following terms can be helpful to describe characteristics of rash:
- erythema: redness
- macule: small, flat, localised area of colour change
- nodule: elevated skin lesion of >0.5cm diameter
- papule: elevated skin lesion of <0.5cm diameter
- petechiae: pinpoint red spots under the skin
- plaque: raised, flat lesion
- pruritis: itch
- purpura: haemorrhagic area in the skin
- pustule: pus-filled lesion
- vesicle: small, fluid-filled blister
The predominant site of the rash should be noted. It is important to document if it is blanching or non-blanching and to look for any field change.
In most circumstances, rashes will be diagnosed on the basis of history and thorough examination. If there is still doubt, investigations should be based on the likely differential diagnosis.
Causes of rash
Medications including sertraline, allopurinol, carbamazepine, lamotrigine and the 'oxicam’ class of anti-inflammatory drugs can cause Stevens-Johnson syndrome, which may start with flu-like symptoms, cough, joint pains and headache and progress to non-pruritic rash with large blisters.
Non-blanching rash will not always develop in meningitis and other symptoms include a high temperature, vomiting, headache, stiff neck, photophobia and unresponsiveness.
Psoriasis presents with red, raised inflamed patches that may have whitish-silver scales or plaques. These may be itchy or painful.
As well as the face, acne can involve the neck, back and chest, and feature papules, pustules, comedones and pseudocysts. Topical antibiotics are usually used in combination, most commonly with benzoyl peroxide.
Impetigo starts with red sores or blisters on exposed areas such as the face and hands. These burst and leave crusty, golden brown patches.
- Medications including NSAIDs and antibiotics
- Atopic eczema
- Acne vulgaris
- Seborrhoeic dermatitis
- Viral infection
- Stevens-Johnson syndrome
- Toxic epidermal necrolysis
- Staphylococcal scalded skin syndrome
- Necrotising fasciitis
Dr Anish Kotecha is a GP in Gwent, Wales.