How to Use Whitening Strips — and Whether to Brush Before or After

To use whitening strips, peel the strip from its liner, place the gel side against your front teeth with the edge along the gum line, fold the rest behind your teeth, and leave it on for exactly the time printed on your box. On brushing: most strip instructions say not to brush just before applying, and it is fine to rinse or brush gently afterwards to remove leftover gel.

Everything else on this page is detail on those two sentences, with the reasons behind each step. The single most important instruction is the one on your own box, because wear times and routines vary widely between products.

Should you brush before or after whitening strips?

Brush after, not immediately before. Crest's guidance says most teeth whitening instructions will tell you not to brush your teeth just before applying the strip, because it helps the strip adhere better. After you take a Crest strip off, its label says you "may rinse or brush to remove remaining gel".

The reason is practical rather than chemical: a strip needs close contact with the tooth to work. If you want clean teeth first, brush earlier and give your mouth time before the strip goes on; your product's own directions are the final word.

After removal, a gentle brush with a soft brush clears the gel. If your teeth feel sensitive, brushing harder will not help; an ordinary soft brush and your usual toothpaste are enough.

Step by step

These steps follow Crest's published directions, which are the most detailed we read. If your product's directions differ, follow yours.

1. Read the box for the wear time and the number of days. Crest says wear times range from 5 minutes to 60 minutes depending on the product, and some are meant to be worn twice a day.
2. Peel the strip from the liner without touching the gel more than you need to.
3. Place the gel side against the teeth, aligned with your gum line, and press for good contact.
4. Fold the rest of the strip behind your teeth and press again.
5. Set a timer. Leave the strip on for the stated time, not longer.
6. Peel from the corner and pull gently across to remove it.
7. Rinse or brush gently to remove leftover gel, and wipe any gel off your gums.

Crest's label adds that you should not eat, smoke, sleep or drink anything except water while wearing its strips, and that you should wash your hands afterwards.

Before your first strip

A few checks before you open the box save most of the disappointment people report. None of them costs anything.

• Look at your front teeth for crowns, veneers or large tooth-coloured fillings. The ADA says only natural teeth can be whitened, so those will stay the colour they are while the teeth around them lighten.
• Check the age guidance. Crest's label says its strips are not intended for children under 12; in the UK and EU, products above 0.1% hydrogen peroxide may not be used on anyone under 18.
• Think about when you last saw a dentist. Crest's label says to ask a dentist first if you need dental work, and a check-up is the moment to find a problem a strip could aggravate.
• Read the strength, if the box gives one. Our ranking of whitening kits notes which sellers publish it.

If any of those gives you pause, a short conversation with a dentist before starting is worth more than any technique below.

How long to leave whitening strips on

Leave strips on for the time your box says, and no longer. Crest's Professional White directions are 45 minutes a day for 20 days; BURST describes 15-minute treatments over a 7-day course; other products sit anywhere between, which is why a general rule would be wrong.

Leaving a strip on longer does not speed things up in a way you control. The ADA lists contact time among the factors that influence tooth sensitivity, and the General Dental Council expects exposure to be limited to the frequency and duration a product is intended for. If you miss a day, pick up where you left off rather than doubling up.

Top and bottom strips

Kits such as Crest's give you separate strips for the upper and lower teeth. Crest's Professional White box holds 40 strips, 20 for the top and 20 for the bottom. Follow your box on whether to wear both at once.

If you only whiten one arch, the colour difference between top and bottom may become noticeable. That is a cosmetic choice, not a safety issue.

Common mistakes that cause problems

Most problems with strips come from the same handful of habits.

• Letting gel sit on the gums. The ADA links gum irritation to improperly applied gel; wipe it off.
• Wearing strips longer than directed to "boost" results, which adds contact time.
• Stacking products, such as strips, a whitening pen and an LED device in the same week.
• Using strips on loose teeth, fillings at the front, or braces. Crest's label says not to use its strips on loose teeth, restorations or braces.
• Pushing through sensitivity. Crest's label says to stop for 2 to 3 days if significant sensitivity or gum discomfort develops, then resume, and to discontinue if it persists.

What to eat and drink during a course

Keep to water while the strip is on; Crest's label says not to eat or drink anything else during use. Beyond that, the ADA lists coffee, tea, red wine, cola, dark fruits and tobacco among the common causes of surface staining, so cutting back on them during a course and after it gives the result a better chance of lasting.

We found no source for a specific waiting time after removal before eating or drinking, so we do not give one. If your product states a wait, follow it.

After the course

Judge the result at the end of the full course, not after the first strip. A study summarised by the ADA found an over-the-counter technique took 16 days to reach the whitening a seven-day tray system produced, so strips are a slow route by design.

If you are unhappy with the result, the answer is rarely another box straight away. Our guide to how often you can use whitening strips covers spacing between courses, and our ranking of the best teeth whitening kits for home use compares products on what they disclose about their strength. If one tooth stayed darker than the others, ask a dentist; the cause may not be one a strip can reach.