Assessment of rash in children

Rash in children is common. The differential diagnoses are extensive, ranging from self-limiting conditions (e.g., roseola) to life-threatening illnesses such as meningococcal disease.

Rash may be the first indication of a potentially serious multi-organ disease or sepsis and should be carefully assessed (see Urgent considerations).

Rash be categorised as maculopapular, pustular, vesiculobullous, diffuse/erythematous, or petechial/purpuric in nature. In many aetiologies these forms may co-exist or evolve from one form to another.

Initial considerations in evaluating a rash in children include its morphology, duration, and distribution. Age, sex, family history, medications, known allergies, and exposures are also of primary importance.

Generally, rash in the absence of fever or systemic symptoms is not urgent.

Definitions

• Macule: a flat area of colour change <1 cm in size (e.g., viral exanthem [such as measles and rubella], morbilliform drug eruption).

• Patch: a large macule >1 cm in size (e.g., viral exanthem [such as measles and rubella], morbilliform drug eruption).

• Papule: a raised area <1 cm in size (e.g., wart).

• Nodule: a larger papule, >1 cm in size (e.g., nodular prurigo).

• Plaque: a flat-topped raised area (a cross between a nodule and a patch; e.g., psoriasis).

• Vesicle: a small fluid-filled lesion (blister) <0.5 cm in size (e.g., varicella, eczema herpeticum).

• Bulla: a larger vesicle >0.5 cm (e.g., bullous impetigo).

• Pustule: a pus-filled lesion (e.g., folliculitis).

• Wheal: a transient raised papule or plaque caused by dermal oedema (e.g., urticaria).

• Scale: flakes of stratum corneum (e.g., eczema, psoriasis).

• Crust: dried serum, blood, or purulent exudate on the skin surface (e.g., impetigo).

• Erosion: loss of epidermis, heals without scarring (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis).

• Ulcer: loss of epidermis and dermis, heals with scarring (e.g., venous ulcer, pyoderma gangrenosum).

• Excoriation: loss of epidermis following trauma such as scratching (e.g., as can be seen in eczema).

• Fissure: a split in the skin (e.g., angular cheilitis, palmoplantar keratoderma).

• Lichenification: thickening of the skin with accentuation of skin markings (e.g., chronic eczema, lichen simplex chronicus).

• Purpura: an area of colour change (red or purple) due to bleeding into the skin; does not blanch on pressure (e.g., vasculitis, disseminated intravascular coagulation).

• Petechia: a pin-point purpuric lesion (e.g., vasculitis, disseminated intravascular coagulation).

• Ecchymosis: a larger area of purpura (e.g., vasculitis, disseminated intravascular coagulation).

• Annular: ringed lesions.

• Malar: also known as ‘butterfly rash’; a symmetrical fixed erythematous maculopapular lesion with slight scale occurring over both cheeks and nose, sparing the nasolabial folds.

This topic covers the assessment of rash in children.

For assessment of rash by lesion type and including adult populations, see Maculopapular rash (Assessment of); Pustular rash (Assessment of); Vesicular-bullous rash (Assessment of).​