Found this online: What is idiopathic guttate hypomelanosis?
Idiopathic guttate hypomelanosis is the name given to 2 to 5-mm flat white spots found on the shins and forearms. ‘Idiopathic' means the cause is unknown, ‘guttate' means resembling tear-drops, and ‘hypomelanosis' refers to the lighter colour of the affected areas.
Who does it affect?
Idiopathic guttate hypomelanosis predominantly affects fair-skinned individuals, but it may occasionally arise in darker skin. Although most often found on the shins and sun-exposed parts of the forearms, guttate hypomelanosis may also arise on other sun exposed areas including the face, neck and shoulders. The white marks are usually smooth with a reduction in the normal skin markings, but they may be slightly scaly.
They appear as part of the aging process, becoming quite common in those over 40 years of age. They are more common in women than in men. Inherited factors may be relevant as the lesions appear to be more common in family members.
It is completely harmless, but won't tan. So - cold weather holdays from now on!