Why Do Teeth Hurt When You're Sick? A Cold and Flu Guide
Clinically reviewed by Dr. Abinaash Kaur, DDS, RCDSO, on 2026-10-30. Dr. Kaur is a general dentist in Toronto (Bloor West Village) registered with the Royal College of Dental Surgeons of Ontario.
Mostly it's your sinuses. The roots of your upper back teeth sit right under the floor of your sinuses, so when a cold stuffs them up, the pressure can make several upper teeth ache at once, and the ache fades as the cold clears.
That's the short answer. The longer one covers everything else a cold or flu does to your mouth: the cough drops, the syrup, the dry mouth, the stomach bug, the toothbrush, and whether you should keep your dental appointment this week.
Flu season is here.
The Government of Canada says your risk of getting the flu "is higher in the late fall and winter" (Government of Canada), and Public Health Ontario says the virus circulates in Ontario "most frequently in the fall and winter" (Public Health Ontario). Every November, my chair fills with people whose teeth started hurting the same week as their nose.
Why do your teeth ache when you have a cold?
Most people think a sore upper tooth during a cold means a cavity showed up at the worst possible time. Here's what's happening instead.
A stuffed nose and a sinus infection travel together. One review of acute sinusitis says most cases follow a blocked sinus opening "associated with the common cold or allergies," and it lists "a maxillary toothache," meaning an ache in the upper teeth, among the signs that help a physician spot a sinus infection (Seminars in Respiratory Infections via PubMed).
Pretty much, your sinus is leaning on your teeth.
The pattern is the clue. In my chair, sinus pain tends to hit several upper teeth at once, feels like pressure, and gets worse when you bend forward or lie flat. One tooth hurting on its own, a tooth that zings with sweet or cold, or a tooth that wakes you at 3 a.m. points at the tooth. Our post on why a toothache gets worse at night walks through how we tell the two apart, and the one on teeth that are suddenly sensitive covers the cold-and-sweet kind.
Most people recover from the flu in 7 to 10 days (Government of Canada). If the tooth ache outlasts the cold, or lands in one tooth, book an exam.
Are cough drops bad for your teeth?
A cough drop is a hard candy with a job. Your teeth don't know the difference.
A cavity starts when bacteria in plaque "digest sugars from foods and drinks that you consume," which "results in an acid that attacks the surface of your tooth" (Government of Canada). A cough drop dissolves slowly, then you reach for another one an hour later. The Ontario Dental Association says snacking through the day on sugary treats "constantly bathes your mouth in sugar," and its plain advice on hard candies is to avoid them (Ontario Dental Association).
Lozenges have been measured.
In a 2025 trial, saliva pH dropped after every lozenge tested, and the mouth took between 12.7 and 19.4 minutes on average to clear back to baseline, depending on the product (Journal of Contemporary Dental Practice via PubMed). The authors concluded that lozenges "with lower pH and prolonged clearance times may pose a higher risk for enamel erosion and caries."
So here's what I'd do on a sore-throat day. Pick the sugar-free kind. Don't tuck a lozenge in your cheek and forget it, and don't fall asleep with one. Rinse with water afterward, which is the Canadian Dental Association's standing advice after anything sugary (Canadian Dental Association).
Sugar-free doesn't always mean tooth-safe. Did you know about this? In a lab study of 30 sugar-free confections, 17 had high levels of food acids and high erosive potential, and 10 of those carried packaging messages suggesting they were safe for teeth (Australian Dental Journal via PubMed). Sour or citrus-flavoured drops are the ones to watch, and water after is still the fix.
Does cough syrup damage your teeth?
It can, the same way a sweet drink can. The Ontario Dental Association puts it directly: "Cough syrups that have a high sugar content may result in tooth decay," and "Medications for children and vitamins can contain higher quantities of sugar" (Ontario Dental Association).
The research on kids backs that up. A 2025 review of 33 studies found that children on liquid medicines for long stretches had "a higher caries risk experience," with a medicine's sugar content and acidity deciding how hard it is on teeth (Health Science Reports via PubMed). A week of syrup for a cold is not a year of it for a chronic condition. The habit still matters.
Which medicine to take, and how much, belongs to your pharmacist and the label. I'm not touching that. What I'll pass on is the Ontario Dental Association's own line: "rinse with water after having sweetened medication" (Ontario Dental Association). If a bedtime dose is sweet, rinse, then brush as usual before bed.
Why is your mouth so dry when you're sick?
Three things gang up on your saliva during a cold. A blocked nose makes you breathe through your mouth, which dries it out. A fever pulls fluid out of you, and the Government of Canada lists "fluids, like water" alongside rest as what helps flu symptoms improve (Government of Canada). Then the medicine cabinet joins in.
The Ontario Dental Association notes that "Antihistamines and antidepressants may cause dry mouth" (Ontario Dental Association), and a clinical review adds decongestants to that list (Journal of Clinical Gastroenterology via PubMed). Saliva is your rinse cycle, and a long-running dry mouth "significantly increases the risk of experiencing dental caries, demineralization, tooth sensitivity" (JADA via PubMed). A week of it won't wreck your teeth. Sip water, skip the sugary throat soothers, and if the dryness stays after the cold leaves, our post on dry mouth and what helps goes deeper.
What should you do for your teeth after a stomach bug?
Rinse first. Brush later. Drink.
Flu can come with "nausea and vomiting," especially in children (Government of Canada), and that puts stomach acid straight onto your enamel. A review of acid wear says that "Immediately after vomiting, patients might be advised to rinse the mouth" (British Dental Journal via PubMed). Plain water, swished and spat.
What gives with the brushing advice?
The Ontario Dental Association says to "Wait at least 30 minutes after eating before brushing," because acid softens enamel and it needs time to re-harden (Ontario Dental Association). The same acid-wear review says "postponing toothbrushing is not clinically advisable" (British Dental Journal via PubMed), and a 2024 scoping review found that in most studies, brushing with a fluoride toothpaste "does not increase" acid wear, whatever the timing (Caries Research via PubMed). The experts are split on the clock, not on the fluoride.
My version is the one we gave in the post on electrolyte powders and enamel: rinse right away, brush gently with fluoride toothpaste when you're up to it, and if waiting means you'll skip brushing, brush. Your hydration comes first. If a doctor or pharmacist told you to rehydrate, do that, and worry about your enamel second.
Should you keep your dental appointment when you're sick?
Have no fear about cancelling. We'd rather you call.
Ontario's dental regulator is clear on this. The Royal College of Dental Surgeons of Ontario says that if office staff "learn that a particular patient has a fever or cough, dental appointments should be rescheduled," and that patients who appear ill should be rescheduled "if at all possible" (RCDSO). Ontario's dental hygiene regulator says the same for influenza: postpone during the contagious period, and rebook "when the person feels well and is non-infectious" (CDHO).
How long is that? The Government of Canada says you can spread the flu "from 1 day before to until about 5 days after your first symptoms," and children and people with weakened immune systems may be contagious for longer (Government of Canada). A cleaning can wait a week. Call and move it.
Pain can't always wait. The regulator's rule for an ill patient whose dental problem is urgent is that "every effort must be made to separate them from other patients" (RCDSO), which is why we ask you to call first rather than walk in. Our guide to what counts as a dental emergency covers where that line sits.
A cold sore is its own appointment question, answered in canker sores, cold sores and your dentist. Spots inside the cheeks with a fever are a different category again, covered in what measles looks like in the mouth.
Some days the schedule pushes us, and a phone call that moves a sick patient to next week is a call I'm glad to get. The person in the next chair has a newborn at home, or chemo on Thursday. Rebooking you protects them.
Do you need a new toothbrush after being sick?
The Ontario Dental Association says yes: "You should also use a new toothbrush after a cold or illness," because "Germs can stay on toothbrush bristles and lead to reinfection" (Ontario Dental Association). That's the advice, and I follow it.
Here's the honest version of the evidence behind it. Toothbrushes do get contaminated: a review found that brushes of healthy and unhealthy adults "become contaminated with pathogenic bacteria from the dental plaque, design, environment, or a combination of factors" (Nursing Research and Practice via PubMed).
Whether that contamination reinfects you is less settled. A systematic review of why strep throat treatment sometimes fails lists "contaminated toothbrushes" among twelve proposed explanations and finds "very little type I or II evidence" for any of them, with most studies "observational (in patients) or laboratory-based without clinical confirmation" (Otolaryngology-Head and Neck Surgery via PubMed).
So a new brush is cheap, harmless, and sensible. It isn't proven to save you from a second round. Swap it once you feel better, which lines up with the Canadian Dental Association's baseline of replacing a brush "when the bristles lose their shape" or "every three months" (Canadian Dental Association). Our toothbrushes 101 post has the rest of the brush advice.
People ask about boiling it or soaking it instead. A 2026 meta-analysis of 41 studies found that chemical soaks, home remedies and UV all cut bacteria on a brush, but rated the certainty of that evidence "very low" (Journal of Evidence-Based Dental Practice via PubMed). A new brush is simpler than a science project.
What matters more while you're sick is keeping your brush to yourself. The Ontario Dental Association's rule number one is "Do not share your toothbrush or use someone else's toothbrush," and it says to rinse, air-dry, and store it upright without the heads touching (Ontario Dental Association). The Public Health Agency of Canada's influenza guidance for home care says the same: give the sick person "their own towel, face cloth, toothbrush, etc.," since the virus "can survive for several hours on environmental surfaces" (Government of Canada).
When should you see a dentist instead of waiting it out?
Sinus pressure in several upper teeth that came with the cold and leaves with it is a physician's or pharmacist's conversation, not mine. The Government of Canada says people at higher risk of flu complications should "contact a health care provider for advice" once symptoms start (Government of Canada).
Book with us when the pain acts like a tooth. One tooth on its own. Pain when you bite down. Swelling in the gum or face. A tooth still hurting after the cold is gone, which is past the 7 to 10 days most people take to recover (Government of Canada). Those are the ones to bring to me, because a cold can hide a cracked tooth or a dying nerve for a week, and neither gets better on its own.
In about 25 years of practising in Bloor West Village, the sick-season tooth I remember most is the one that "started with my cold" in November and turned out to be an abscess that had been quietly building since summer. The cold didn't cause it.
The cold just got the blame.
Frequently Asked Questions
Q: Is it normal for your teeth to hurt when you have a cold or the flu? Yes, especially the upper back teeth. Their roots sit under the sinus floor, and a review of acute sinusitis lists "a maxillary toothache," an ache in the upper teeth, among the signs of a sinus infection, most of which follow the common cold (Seminars in Respiratory Infections via PubMed). It should fade as the cold clears.
Q: Do cough drops cause cavities? They can. A cough drop is sugar dissolving slowly against your teeth, and the Ontario Dental Association says snacking through the day on sugary treats "constantly bathes your mouth in sugar" (Ontario Dental Association). In a 2025 trial, every lozenge tested dropped saliva pH, and clearance took 12.7 to 19.4 minutes (Journal of Contemporary Dental Practice via PubMed). Sugar-free, then water.
Q: Are sugar-free cough drops safe for teeth? Safer, not automatically safe. In a lab study of 30 sugar-free confections, 17 had high acid content and high erosive potential, and 10 of those had packaging suggesting they were tooth-safe (Australian Dental Journal via PubMed). Sour and citrus flavours are the ones to rinse after.
Q: Can I go to the dentist with a cold? Call first and expect to rebook. The Royal College of Dental Surgeons of Ontario says that when staff learn a patient "has a fever or cough, dental appointments should be rescheduled" (RCDSO). If you're in pain or swelling, say so on the phone; urgent problems are handled differently from a cleaning.
Q: Should I replace my toothbrush after strep throat or the flu? The Ontario Dental Association says to use a new toothbrush after a cold or illness because germs can stay on the bristles (Ontario Dental Association). The direct evidence that an old brush reinfects you is weak; a systematic review on strep treatment failure found "very little type I or II evidence" for that explanation (Otolaryngology-Head and Neck Surgery via PubMed). It's cheap, so swap it.
Q: Should I brush my teeth right after throwing up? Rinse with water right away, which a review of acid wear says patients "might be advised" to do immediately after vomiting (British Dental Journal via PubMed). The Ontario Dental Association advises waiting at least 30 minutes after eating before brushing (Ontario Dental Association), while a 2024 review found brushing with fluoride toothpaste "does not increase" acid wear whatever the timing (Caries Research via PubMed). Rinse first; brush when you're up to it.
Reviewed by Dr. Abinaash Kaur, B.Sc., DDS (University of Toronto Faculty of Dentistry), who has practised general and family dentistry in Bloor West Village for about 25 years. This article is general oral health information, not a diagnosis or a substitute for an examination. Questions about cold and flu medicines belong with your pharmacist or physician.
Tooth still hurting after the cold is gone, or one tooth that never joined the sinus ache? We're at 750 Annette Street in Bloor West Village, serving the Junction, High Park, and Baby Point. Book a visit with The Village Dentist and we'll find out whether it was ever the cold at all.
