Melasma is a medical expression (see also: chloasma) to describe what you and I would probably call pigmentation. is most common in women between the ages of 20 and 40 and usually affects the cheeks, bridge of the nose, forehead and upper lip. Causes are various, though very often the condition is caused by hormonal changes or fluctuations that occur during pregnancy which is why this complaint is sometimes referred to as a "pregnancy mask". The dark patches are also brought on by sunlight, though even artificial light can cause the brown patches to develop. It is not really dangerous or painful but it is often a highly distressing condition for those who suffer from Melasma.
One temptation to avoid is high intensity (e.g. fraxel) lasers. Many will suggest that these lasers can get rid of the pigmentation however, in many, if not most cases, the use of these lasers can aggravate the condition and cause it to spread. In the same way, sunscreen is vital to prevent the spread and a high factor sunscreen is always to be used; even where the sun appears or seems to be fairly weak.
Care should be taken with skin care products used. The skin should be treated as "sensitive" and beware any products containing a high content of any form of acids (AHA's etc) as these strong products, again, can aggravate the condition. Certainly, if you ever have a burning sensation when using any product - stop.
Diet can help and if required, include supplements which would include Vitamin C, Vitamin A as well as glutathione. Vitamin C in skin care products should also help as studies have been made to show that Vitamin c does, indeed, help the condition.
You are, of course, reminded that if you do have this sort of pigmentation then it is time to visit your chosen healthcare professional; and certainly before you follow any advice involving which skin care products to use. If you need to find a skin care professional, please go to the BCAM website. (British College of Aesthetic Medicine) where you can find a registered professional near you.