Is It Safe to Use Someone Else’s Toothbrush? A Doctor Weighs In

Berlin — We’ve all been there: you’re traveling, you forget your toothbrush and the only one within reach belongs to your partner, roommate, or family member. In a moment of desperation, you might wonder: Is it really that terrible to borrow someone else’s toothbrush? According to dental experts, the answer isn’t as simple as a yes or no. While sharing a toothbrush in an emergency might seem harmless, the risks—particularly from harmful bacteria like Streptococcus mutans—are real and worth understanding.

Dr. Samantha Byrne, an associate professor in oral biology at the University of Melbourne, estimates that about half of people have shared a toothbrush at some point, often between spouses or parents and children. But just because it’s common doesn’t indicate it’s safe. The mouth is home to hundreds of bacterial species, some of which can cause tooth decay, gum disease, and even systemic health issues if they enter the bloodstream. So, what exactly happens when you use someone else’s toothbrush—and when, if ever, is it acceptable?

To answer these questions, we spoke with dental experts, reviewed recent research, and examined the science behind oral bacteria. Here’s what you need to know.

The Science Behind Oral Bacteria: What Lives in Your Mouth?

The human mouth is a thriving ecosystem, hosting more than 700 different bacterial species, though most people typically have around 200 species at any given time, according to research published in Frontiers in Microbiology. While many of these bacteria are harmless—or even beneficial—some can pose serious risks to oral and overall health.

The most concerning bacteria include:

• Streptococcus mutans: The primary culprit behind tooth decay, this bacterium thrives on sugars and produces acids that erode tooth enamel. A 2024 study in Frontiers in Microbiology highlighted its role not just in cavities but also in broader health issues, including inflammation and even cardiovascular risks when it enters the bloodstream through gum disease. The study, led by researchers at Sichuan University and the University of Hong Kong, noted that S. Mutans’s ability to produce glucosyltransferases—enzymes that assist it stick to teeth—makes it particularly adept at forming plaque and initiating decay (source).
• Porphyromonas gingivalis: A key player in gum disease, this bacterium can trigger inflammation and has been linked to conditions like diabetes and Alzheimer’s disease. Research from the Journal of Periodontology shows that it can survive on toothbrush bristles for days, increasing the risk of transmission when brushes are shared.
• Treponema denticola: Another bacterium associated with gum disease, it works alongside P. Gingivalis to break down gum tissue and contribute to periodontal disease.

Dr. Byrne explains that these bacteria aren’t just confined to the mouth—they can also live on toothbrushes. “The three species mentioned above have been found to survive on toothbrush bristles, which means sharing a toothbrush could expose you to harmful pathogens,” she told ABC News in a recent interview. While good oral hygiene and a balanced diet can mitigate many of these risks, sharing a toothbrush introduces an additional layer of vulnerability.

What Happens When You Share a Toothbrush?

When you use someone else’s toothbrush, you’re not just transferring bacteria—you’re also exposing yourself to viruses, fungi, and other microorganisms that may be present in their mouth. Here’s particularly concerning for individuals with weakened immune systems, chronic illnesses, or open wounds in the mouth (such as cuts from braces or recent dental work).

Here’s what can happen:

• Increased Risk of Tooth Decay: If the toothbrush owner has high levels of S. Mutans, you could be introducing more of these cavity-causing bacteria into your own mouth. Over time, this can accelerate plaque formation and increase the likelihood of cavities.
• Gum Disease Transmission: Bacteria like P. Gingivalis and T. Denticola can trigger gingivitis (early-stage gum disease) or periodontitis (a more severe form that can lead to tooth loss). Sharing a toothbrush with someone who has gum disease could transfer these bacteria to you, even if you’ve never had gum issues before.
• Viral Infections: While less common, viruses like herpes simplex (which causes cold sores) or even the flu virus can survive on toothbrush bristles. If the toothbrush owner is sick, you could inadvertently expose yourself to their illness.
• Systemic Health Risks: Emerging research suggests that oral bacteria can enter the bloodstream through inflamed gums, potentially contributing to heart disease, diabetes complications, and even pregnancy risks. A 2023 study in Scientific Reports found that P. Gingivalis was present in the arterial plaques of patients with atherosclerosis, suggesting a possible link between gum disease and cardiovascular health (source).

Dr. Byrne emphasizes that these risks are higher for certain groups, including:

• People with compromised immune systems (e.g., those undergoing chemotherapy or living with HIV/AIDS).
• Individuals with diabetes, which can make them more susceptible to infections.
• Children, whose immune systems are still developing.
• Anyone with open sores or cuts in the mouth.

When Is It “Okay” to Share a Toothbrush?

Despite the risks, there may be rare situations where sharing a toothbrush is the lesser of two evils. For example, if you’re stranded without your own toothbrush and forgoing oral hygiene entirely would lead to worse outcomes—such as severe bad breath, plaque buildup, or an increased risk of cavities—using someone else’s toothbrush once might be a temporary solution. However, experts agree that this should be an absolute last resort.

If you find yourself in this situation, Dr. Byrne offers the following advice to minimize risks:

• Rinse Thoroughly: Before and after use, rinse the toothbrush with hot water to remove as much bacteria as possible. Some experts also recommend soaking the brush in mouthwash for 30 seconds to kill additional germs.
• Avoid Sharing with Sick Individuals: If the toothbrush owner is ill—especially with a contagious virus like the flu or COVID-19—do not use their toothbrush under any circumstances.
• Replace the Toothbrush ASAP: If you’ve used someone else’s toothbrush, replace it as soon as possible. The American Dental Association (ADA) recommends replacing toothbrushes every 3–4 months, or sooner if the bristles are frayed or if you’ve been sick (source).
• Use a Finger as a Temporary Solution: If you don’t have a toothbrush, Dr. Byrne suggests using your finger with a dab of toothpaste as a short-term alternative. While not ideal, it’s safer than sharing a toothbrush and still helps remove some plaque and bacteria.

For parents, the rules are slightly different. Many pediatric dentists acknowledge that parents may occasionally use their child’s toothbrush to clean their teeth in a pinch, especially for very young children who can’t brush effectively on their own. However, this should be a rare exception, not a habit. “If you’re going to share a toothbrush with a child, make sure it’s a one-time thing and replace the brush afterward,” advises Dr. Ruchi Sahota, a spokesperson for the ADA.

How to Retain Your Toothbrush Clean and Safe

Even if you never share your toothbrush, it’s important to keep it clean to avoid reintroducing bacteria into your mouth. Here are some expert-recommended tips:

• Store It Properly: After brushing, rinse your toothbrush thoroughly with water and store it upright in an open-air holder to allow it to dry. Avoid covering it or storing it in a closed container, as moisture promotes bacterial growth.
• Don’t Share Containers: Even if toothbrushes aren’t touching, storing them in the same container can lead to cross-contamination, especially if one person is sick.
• Sanitize Occasionally: While the ADA states that regular rinsing is sufficient for most people, you can sanitize your toothbrush by soaking it in mouthwash or a 3% hydrogen peroxide solution for a few minutes. Some toothbrush sanitizers use UV light to kill bacteria, though their effectiveness varies.
• Replace It Regularly: As mentioned earlier, replace your toothbrush every 3–4 months, or sooner if the bristles are frayed. If you’ve been sick, replace your toothbrush immediately after recovering to avoid reinfection.
• Travel Smart: When traveling, pack your toothbrush in a ventilated case to keep it dry. Avoid using hotel-provided toothbrushes unless absolutely necessary, as their storage conditions are often unknown.

Key Takeaways: What You Need to Remember

• Sharing a toothbrush is risky, even in emergencies. The mouth harbors hundreds of bacterial species, some of which can cause tooth decay, gum disease, and even systemic health issues.
• Bacteria like Streptococcus mutans, Porphyromonas gingivalis, and Treponema denticola can survive on toothbrush bristles, increasing the risk of transmission when brushes are shared.
• Certain groups are at higher risk, including people with weakened immune systems, diabetes, or open wounds in the mouth. Children and the elderly should also avoid sharing toothbrushes.
• If you must share a toothbrush, rinse it thoroughly before and after use, avoid sharing with sick individuals, and replace the toothbrush as soon as possible.
• Better alternatives exist, such as using your finger with toothpaste or purchasing a disposable toothbrush from a pharmacy.
• Proper toothbrush hygiene—such as storing it upright, replacing it regularly, and avoiding shared containers—can help reduce bacterial buildup.

The Bottom Line: Is It Ever Worth the Risk?

While sharing a toothbrush once in a blue moon is unlikely to cause immediate harm, the long-term risks—especially for vulnerable individuals—far outweigh the temporary convenience. Oral health is closely tied to overall health, and practices like sharing toothbrushes can undermine the efforts you make to keep your mouth clean and healthy.

If you find yourself without a toothbrush, consider these safer alternatives:

• Use your finger with a dab of toothpaste to clean your teeth.
• Purchase a disposable toothbrush from a pharmacy or convenience store.
• Question your hotel or host for a spare toothbrush—many provide them upon request.
• In a pinch, chew sugar-free gum to stimulate saliva production, which helps neutralize acids and wash away food particles.

As Dr. Byrne puts it, “Good oral hygiene is about consistency. While using someone else’s toothbrush once might not cause immediate problems, it’s not a habit you want to make. Your mouth—and your health—will thank you for keeping your toothbrush to yourself.”

For more tips on maintaining oral health, check out our guide on best practices for oral hygiene or learn about how to prevent gum disease.

Have you ever shared a toothbrush? What’s your go-to solution when you forget yours? Share your thoughts in the comments below—and don’t forget to brush (with your own toothbrush)!