The change in colour may result from pigment
loss or excess, erythema, or haemorrhage. Erythematous
macules are common in inflammatory diseases of the superficial
dermis, such as allergies.
Petechiae are pin-point macules caused
by haemorrhage of less than 1 cm in diameter. Ecchymoses
are patches caused by haemorrhage of more than 1 cm in diameter.
Cutaneous haemorrhages may reflect thrombocytopenia,
defects in coagulation, or vasculitis.