A bluish stain on the skin caused by the bites of fleas or lice located primarily on the chest, abdomen, thighs, and upper arms noticeable in light-skinned individuals: Maculae ceruleae are probably the result of altered blood pigments in infested individuals, or to an excretion product in the louse's saliva that converts bilirubin (a reddish-yellow bile pigment) to biliverdin (a green pigment occurring in bile).

The public health nurse noticed the presence of macula ceruleae among her street or homeless clients and reported this to the local health authorities.