I wanted to add that the most common cause of these "white patches" of skin is Pityriasis alba. It usually presents as dry, fine-scaled patches on the face. Moisterizing is all that is required.
The condition is seen mostly in children aged 2 - 16 years. It is occurs more often in light skinned individuals but it is more noticeable in darker complexions. It is most noticeable during the dry winter months as a result of dry air. In the summer, tanning of surrounding normal skin may make the paatches more prominent.
Lesions tend to be round or oval (0.5 - 2cm) but on the body they can be up to 4cm - they tend to number from 4 to over 20. They occur most commonly on the face (cheeks), but they can appear on the arms, neck or shoulders.
There isn't a treatment, they usually settle with time. If there is any redness or itchiness associated with them than hydrocortisone may be aplied.
Commonly the patches last for about 1 year.
This is a pretty benign condition and with proper moisterizing resolves on its own. In any case, white patches are more likely to be pityriasis rather than vitiligo (which is an autoimmune condition in which the immune system targets melanin) - but a doctor should be seen to determine what the patches are.
My son currently has a little pityriasis alba, but because his complexion has lightened significantly with exjade it is not very noticeable.
I hope this helps,
Sharmin