There are various technical terms that are used to describe rashes. Though it is not strictly necessary for a parent or care giver, for example, to know specific technical terms when describing a rash, it helps in understanding diagnoses, treatment and liaising with other medical staff.
The key to sufficiently describing a rash is to observe carefully and closely the affected area.
The ‘ordinary’ meanings of some technical terms that are used to describe rashes are given below.
The term ‘erythema‘ simply means ‘red’.
A ‘macule‘ is a small, flat area (or ‘spot’) of discoloured skin (usually less than 5 mm in diameter).
A ‘papule‘ is a small, raised area of skin (less than 5 mm). It usually has a domed top (although it can be flat).
The term ‘maculopapular‘ refers to a combination of small flat ‘spots’ and raised ‘spots’ on the skin. This sort of rash is typical of measles.
A ‘vesicle‘ is a papule (see above) with a fluid-filled centre. Vesicles are typical of chickenpox rash and ‘cold sores’.
A ‘pustule‘ is a vesicle (see below) containing yellow fluid. This fluid usually consists of serum (blood fluid), white blood cells, and the virus that has caused the original infection. The presence of a pustule does NOT mean that the rash has ‘become infected’ with bacteria; pustules are an ‘expected’ event in many viral illnesses.
A ‘nodule‘ is a larger swelling on the skin surface (usually more than 5 mm in diameter). It extends deep into skin, and is usually firm to the touch.
Petechiae (pronounced ‘p-TEEK-ee-eye’) are small, red-brown, flat macules (see above) up to 2 mm in diameter. It is important to note that they do not blanch (turn white) when pressure is applied with a finger — in contrast to most rashes in children which DO fade when pressure is applied. Petechiae are caused by tiny spots of blood gathered under the surface of the skin. They are important in diagnosing meningococcal disease and other conditions. Anyone with a non-blanching rash needs to see a doctor promptly.
‘Purpura‘ means areas of little petechiae joined together. These are therefore larger areas (usually more than 2 mm) of bleeding under the skin.