I answered your post in the peels portion of the forum. Here is a repost:
"Hydroquinone can be dangerous if used incorrectly or if you have an adverse reaction and continue to use it. It has been positively linked to certain conditions from dermatitis to yes, cancer.
It has been known to be an effective treatment. Many use it for melasma.
Sun exposure can be problematic with this product, especially at first, so take it easy with the outdoor activities for a bit if possible.
If you are closely monitored by your doctor (i.e.: blood tests, overall physical examinations, etc.) you stand a better chance of having good results with this product."