The reason for these white spots is not clearly known (Idiopathic).
The spots (macules) are 'drops' like (guttate), small in size (2-5 mm) and hypopigmented (hypomelanosis).
In some cases lesions measuring up to 10 mm diameter have been observed.
The causes for these white spots is not completely investigated and it is believed that sun exposure causes it.
It is further believed that the UV range of the sunlight could be the culprit.
These tiny white spots are usually formed on the forearms and shin regions of the body which are usually exposed more to sunlight.
They may also form on the other exposed parts of the body like shoulders, neck and face.
These white spots have been found to affect far more women than men.
Fair skinned people are found to be affected more frequently and at a younger age.
This disorder usually begins around the age of 30 years and it is also believed to be the part of the aging process.
Idiopathic guttate hypomelanosis, typically develops on the legs, more particularly on the shins of the fair-skinned women in their early thirties.
Later idiopathic guttate hypomelanosis slowly progresses to cover forearms, shoulders and neck.
A familial (genetic) acquirement of these idiopathic guttate hypomelanosis white spots has been noted, requiring further research in this aspect.