Why is my tongue white on the top?

I am sorry to hear that your tongue appears white, and that it is worrisome for you. There are many possibilities as to what might be going on. I would suggest starting out by making an appointment with an otolaryngologist (Ears Nose and Throat aka ENT) physician to be evaluated. They would be one of many specialties that would be comfortable in diagnosing oral pathology. Also while I can give you some of my best guesses as to what might be going on, they will be able to examine you and give a more specific, directed answer. As I mentioned earlier, there are many different processes that can give you a whitish tongue. One of the more common ones is called oral thrush (or oral candidiasis). This is a fungal infection (candida) involving the lining of the tongue. It is seen most frequently in immunocompromised patients, but can also be found in patients that use steroid inhalers for pulmonary disease (asthma, COPD, etc). It is typically able to be scraped off the surface, leaving behind an erythematous (inflamed/red) surface. This is typically easily treated with oral anti-fungal medications. If the whitish stuff doesn't scrape off, you have have leukoplakia (literally means white plaque) which can be a benign process. At this point I wouldn't necessarily be worried, but if the lesion doesn't go away after a week or two, I would get checked out by an otolaryngologist. I hope this information was helpful. Best of luck.