As many people who have used teeth whitening products can attest, they can lead to some soreness and sensitivity in exchange for whiter teeth. It is completely normal to have sore teeth after using teeth whitening products. The soreness is temporary and should not last longer than a few days after the whitening process is completed.
It is not entirely clear what causes this sensitivity in over two-thirds of people who use either at-home whitening methods or get professional whitening at the dentist. However, it is believed to occur when the peroxide used for bleaching comes into contact with the nerve tissue inside the tooth. Nearly all tooth whitening systems use peroxide as the active bleaching ingredient, which leads to temporarily sore teeth or sore gums.
There are different types of tooth whitening systems. You may use dental trays, strips that stick on your teeth, or a gel that is painted on with a brush. Some are used for as little as five days, while others are used for two weeks to a month. There are also daily teeth whitening kits, which are generally applied for a few minutes a day every day. Any of these methods can cause sore teeth.
In most cases, the level of soreness is in direct proportion to the percentage of peroxide used. In at-home whitening kits, the percentage of peroxide is displayed on the kit -- so choosing a kit with a lower percentage of peroxide should help to prevent some sensitivity. In general, the faster the process, the higher the level of peroxide. Professional whitening at the dentist has the highest amount of peroxide, but also generally takes the least amount of time, which can actually be helpful for those prone to sensitivity and sore teeth.
If you've completed a tooth whitening system and are experiencing sensitivity, some suggest applying fluoride to the teeth to lessen the pain. Another option that can help is to brush your teeth with a toothpaste designed for sensitive teeth. The pain should dissipate within a day or two after you've finished the bleaching system; if the pain is severe, or the sore teeth do not improve, you should contact your dentist.
If your teeth are too sensitive for whitening, some people find success using whitening toothpaste, which usually contains gentle abrasives to clean surface stains, but not peroxide. Mouthwash that promises to whiten teeth also exists. For a natural method with virtually no danger of sore teeth, brushing with baking soda is effective and gentle. Never brush your teeth with lemon juice or strawberries, two popular "natural" methods, as these methods can strip the enamel off your teeth, leading to not only sore teeth but also permanent damage and tooth decay.