Whitening your teeth is a great way to improve the appearance of your smile for relatively little effort. However, it's important to remember that when whitening your teeth less is more!
When someone over-whitens their teeth, the result can be quite jarring. Blindingly white teeth are not very attractive, and can look quite weird in person.
Unless you have a career in the public spotlight such as television, or perhaps modelling, it’s always better to err on the side of caution when whitening your teeth. Remember that over-doing teeth whitening can have the opposite of the intended effect: it could make your smile less attractive.
Additionally, over-whitening your teeth can lead to dental health problems. It can soften your enamel, making your teeth extra sensitive, and in some extreme cases, it might even cause your teeth to become a strange blue-grey colour.
That being said it takes a lot of over-whiten your teeth to the extent that you wind up with oral health problems and teeth whitening is generally considered to be very safe.