Childhood exanthems vary greatly depending on factors such as location, size, elevation, palpability and the content of the associated skin eruptions.
Seven broad types have been identified:
A macule is a circumscribed area of change in normal skin colour, with no skin elevation or depression. It may be any size.
A papule is a solid raised lesion up to 0.5 cm in greatest diameter.
Note, however, that some text definitions use 1.0 cm as a cut-off limit instead of 0.5 cm.
A nodule is similar to a papule but is located deeper in the dermis or subcutaneous tissue.
Nodules are differentiated from papules by palpability and depth, rather than size.
A plaque is an elevation of skin occupying a relatively large area in relation to its height.
It can often be formed by a confluence of papules.
A pustule is a circumscribed elevation of skin containing purulent fluid of variable character.
The fluid may be white, yellow, greenish or haemorrhagic.
A vesicle is a circumscribed, elevated, fluid-containing lesion less than 0.5 cm in its greatest diameter. It may be intra-epidermal or sub-epidermal in origin.
Note, however, that some text definitions use 1.0 cm as a cut-off limit instead of 0.5 cm.
A bulla is similar to a vesicle, except the lesion is more than 0.5 cm in its greatest diameter.
Note, however, that some text definitions use 1.0 cm as a cut-off limit to replace 0.5 cm.