For most people, whitening is not painful in the way a drilled filling can be. What many do notice is sensitivity: a brief, sharp twinge in a tooth, or a dull ache and a stronger reaction to cold, starting during treatment or later the same day. In the classic early trial of tray whitening, about two in three people had some side effect, and those side effects settled within 24 to 48 hours.
So the realistic expectation is some discomfort for some people, usually short-lived, and largely controllable with the right gel, the right timing and a little preparation.
Two different sensations, from two different places
Tooth sensitivity during whitening is often described as a sudden jolt in one tooth that arrives without any trigger, lasts a second or two and goes. Other people feel a more general ache, or find that a glass of cold water suddenly feels icy.
Gum irritation is something else. It happens where gel touches the gum, usually at the edge of a tray or strip, and often shows up as a small white patch that is a little sore and fades within hours. It is managed by using less gel and wiping away any excess, not with the steps used for tooth sensitivity.
Peroxide has to travel through the tooth to work
Whitening gels contain hydrogen peroxide, or carbamide peroxide, which breaks down to release hydrogen peroxide. To lighten the tooth, the peroxide passes through the enamel into the dentine underneath and breaks down the coloured compounds there. Some of it reaches the pulp, the nerve and blood supply in the middle of the tooth.
Exactly how that produces pain is still not settled. In a 2010 paper in Medical Hypotheses, Markowitz pointed out that whitening pain can strike healthy, intact teeth with no stimulus at all, which differs from ordinary sensitivity, and proposed that peroxide may switch on a receptor on the pulp nerves directly. If that is right, treatments that calm nerve activity, such as potassium salts, would be the logical choice for relief. Either way, in a healthy tooth the reaction is usually temporary and fades once the peroxide is gone.
Teeth also dry out slightly during whitening, and a drier tooth reacts more to temperature for a while. That is part of why cold drinks can feel sharper on the evening after an in-chair session.
Take-home whitening tends to be gentler, and easier to adjust
In-chair whitening applies a stronger gel for a shorter time, with the gums protected by a barrier. Most people feel little in the chair. If sensitivity comes, it tends to arrive that evening.
Take-home whitening uses a lower-strength gel in custom trays over a series of sessions. Sensitivity, if it appears, usually builds gradually and can be managed by skipping a session or shortening wear time, which is not possible once an in-chair session is under way.
The research leans the same way, with caveats. A 2016 meta-analysis in Operative Dentistry by de Geus and colleagues found no clear difference between the two methods in the risk or intensity of sensitivity. Their 2025 update, with more trials, found that intensity was lower with at-home whitening, while the chance of having any sensitivity was similar. The authors rated the evidence as low quality, so the fairest reading is that home whitening may be gentler, not that it always is. At Lumi, all three options include Boutique take-home whitening with custom trays, and Lumi Home offers an overnight gel made for sensitive teeth and a daytime gel for teeth that are not sensitive.
Some teeth are more likely to react
Sensitivity is more likely if your teeth already react to cold or sweet food, if gums have receded and left root surfaces exposed, or if enamel is worn near the gum line. Cracks, leaking fillings and decay can give gel a direct path to the nerve. A strong gel, long wear times or starting a new course too soon after the last one also raise the odds.
Exposed roots change the plan, and our article on whitening with receding gums explains how. Decay and faulty fillings should be fixed before any gel is used, for the reasons covered in whitening with cavities or untreated decay.
Small changes that make whitening more comfortable
Prepare the teeth first. A 2015 meta-analysis in the Journal of Dentistry (Wang and colleagues) found that desensitising agents containing potassium nitrate and sodium fluoride reduced sensitivity during whitening. Many dentists suggest brushing with a potassium nitrate toothpaste for a week or two before you start and carrying on during treatment. Spit out the excess rather than rinsing, so more stays on the teeth.
Use a small amount of gel. A small dot in each tooth space of the tray is enough. More gel does not whiten faster. It mainly ends up on the gums.
Spread it out. If a tooth starts to twinge, wear the trays for less time or whiten every second night. The result depends on the total time the gel spends on the teeth, so spacing sessions usually just means finishing a little later.
Use the trays for relief too. A desensitising gel can be worn in the same custom trays on nights off or around whitening sessions, which is one practical advantage of professional trays.
Go easy on temperature. Lukewarm drinks are kinder for a day or two after an in-chair session or a run of home sessions.
Before recommending a gel, the dentist checks for existing sensitivity, gum recession and fillings. Our guide to Lumi Home take-home whitening explains the take-home part, and the teeth whitening page sets out all the options.
Pain that lingers is a reason to stop and get checked
Whitening sensitivity comes and goes. See a dentist or oral health therapist if you have pain that lasts more than a few moments after a hot or cold drink, a throbbing ache or pain that wakes you, one tooth that stays sensitive for days after you stop, or pain when you bite on a particular tooth. These point towards a crack, decay or an inflamed nerve that was already there and has been brought to light. Our article on how long sensitivity lasts after whitening describes the usual pattern in more detail.
Common questions
Can whitening damage the nerve permanently?
For most people with healthy teeth, the sensitivity from professional whitening is temporary. The pulp is not immune, though: one small study found that a 38% hydrogen peroxide gel left on for 45 minutes damaged the pulp of lower front teeth, which is one reason gel strength and timing are chosen carefully. Lasting pain usually means something else needs attention. Our article on whether whitening damages enamel covers the outer surface of the tooth.
Will a desensitising toothpaste weaken my result?
It is not expected to. Potassium nitrate works on the nerve rather than on the stain. In the Wang review, colour results with desensitisers were inconsistent across studies rather than clearly worse.
My teeth are already sensitive. Can I still whiten?
Often, once the reason for the sensitivity is known. Exposed roots, worn enamel and decay are each handled differently, and a lower-strength take-home gel with spaced sessions suits many people.
If you would like your teeth checked before deciding, current whitening options and our free cosmetic consult are on the current deals page.
