While the solutions for the most common types of sensitivities caused by peroxide teeth whiteners are usually simple, the potential for side effects is one of the primary reasons why it makes so much sense to communicate with your dentist about your teeth whitening activities. Your dentist can be an invaluable resource when trying to determine if the side effects you are experiencing fall within the realm of normal, and also in determining what solutions exist for resolving them.
If the side effects you experience become problematic then the most prudent thing you can do is cease your teeth whitening treatments. The sensitivities that are most commonly associated with the use of peroxide-based teeth whiteners usually subside within a few days of having terminated the bleaching process. Now is your time to experience this relief. Stop your bleaching activities and let things return to normal.
For the most part the process of peroxide teeth whitening is simply cause and effect. The whitening you achieve is the result of the cumulative effect of the whitening treatments you perform. If sensitivity is a problem for you then you may find that bleaching for a shorter duration or even bleaching every other day can be a solution. The total amount of time (days) that it will take for you to whiten your teeth will be greater, but the aggravation you experience with side effects will most likely be reduced.
The potential any peroxide-based teeth whitener has to cause side effects is thought to be concentration related. If experiencing sensitivity has become a problem for you then possibly whitening with a bleaching agent that has a lower concentration of peroxide will produce fewer complications. While stronger concentrations are sold, 10% carbamide peroxide (which creates a 3.5% hydrogen peroxide bleaching solution) used in a custom bleaching tray is still the unofficial standard for at-home teeth whitening and is generally considered to put the user at less risk for side effects than higher concentration whiteners.
Especially in the case where stock bleaching trays are used, applying an excessive amount of whitener will allow the gel to express to the areas where the tray rests on the user's gums. This can certainly be a cause of gum irritation. Peroxide-based teeth whitening is thought to involve "thin-film" chemistry. This means it doesn't take a lot of whitener to produce results. You just need to use enough to cover the front side of the teeth being whitened.
Tooth thermal sensitivity (a sensation experienced in response to either hot or cold foods and beverages) is a common side effect associated with the use of peroxide-based teeth whiteners. A simple remedy for thermal sensitivity can be the use of a toothpaste labeled and marketed as being a treatment for "sensitive teeth". Pretty much all big name toothpaste manufacturers make this type of toothpaste. There are also some specialty brands selling this type of product. The active ingredient in these toothpastes is usually potassium nitrate.
Stock bleaching trays (as opposed to custom fabricated trays created by a dentist) can be ill fitting, even to the point of placing excessive pressure on teeth and gums. This pressure can cause tooth sensitivity or pain, lead to creating tooth movement (just like braces do), or possibly even cause gum recession. If you find that you feel pressure when wearing your bleaching tray you possibly are putting yourself at risk. The tray's fit should be evaluated before a serious problem occurs.
Toothpastes that contain the detergent sodium lauryl sulfate (often abbreviated "SLS") may contribute to the creation of side effects caused by peroxide-based teeth whiteners. "SLS" has the ability to denature proteins. It has been postulated that this action can allow a greater penetration of peroxide bleaching agent into a tooth, thus resulting in tooth sensitivity.
You will find that the formulations of the vast majority of toothpastes do contain sodium lauryl sulfate. When shopping you must specifically look for toothpaste that is labeled as being "SLS free".