Primary or idiopathic pigmentations

The primary or idiopathic pigmentations result from the application of irritants, which set up hyperaemia in some cases and in others not - as after the action of heat - or friction, or irritants, such as mustard plasters, or the pressure on a part, as by dresses, mechanical restraints, the friction of straps, and the following of certain handicrafts by which certain parts of the body are exposed to the sun or specially rubbed, as in masons. Scratching also will be followed in some cases by discoloration - this is seen in phtheiriasis particularly.