Abnormal skin colours
These may be caused by an imbalance of the normal pigments mentioned above (e.g. in cyanosis, chloasma and carotenaemia) or by the presence of abnormal pigments (Table 17.1).
Sometimes it is difficult to dis-tinguish between the colours of these pigments; e.g. the gingery brown colour of haemosiderin is readily confused with melanin. Histological stains may be needed to settle the issue. In practice, apart from tat-toos, most pigmentary problems are caused by too much, or too little melanin.
Decreased melanin pigmentation
Some conditions in which there is a lack of melanin are listed in Table 17.2.