Why there are bacteria in your mouth
The mouth is warm, moist and always supplied with food, so it hosts a huge community of microbes, called the oral microbiome. Every healthy mouth has one, including the germs in the mouth of a person who brushes carefully. This is normal and not a sign of poor hygiene.
Many of these bacteria help. They compete with harmful species for space, take part in digesting food and help keep the balance of the mouth stable. A healthy balance keeps the troublemakers in check.
When bacteria become harmful
Trouble starts when plaque, the sticky layer of bacteria on the teeth, is left undisturbed. Some bacteria feed on sugar and produce acid, which dissolves enamel and causes cavities. Others thrive under the gum line, where they inflame the gum and, over time, damage the bone. See our guide on what plaque is.
Bacteria on the back of the tongue and between the teeth also release smelly gases, which is a common source of bad breath. Frequent sugar, a dry mouth, tobacco and skipped cleaning all shift the balance towards the harmful kinds.
Should you try to kill the bacteria in your mouth?
No. Strong antiseptic rinses used constantly do not remove plaque, and wiping out bacteria wholesale disturbs the balance and can leave the mouth dry or stained. The practical goal is to remove plaque regularly, so the harmful bacteria never build up. Brushing twice a day, cleaning between the teeth and the tongue, and limiting sugar do this.
Details are in our guides on tooth care and what is oral hygiene. Visit a dentist for a professional clean if you notice bleeding gums, a persistent bad taste or bad breath that does not go away. Infection that spreads, with swelling of the face, fever, or difficulty swallowing or breathing, needs same-day care, and a hospital emergency department if breathing or swallowing is affected.
Common questions
How many bacteria are in the mouth?
Far too many to count in practice. A healthy mouth contains hundreds of species, and each tooth can carry a huge number of bacteria in plaque. That is normal. What matters is the balance and how well plaque is cleaned away, not the total.
Does mouthwash kill the bacteria in your mouth?
Some antiseptic mouthwashes reduce bacteria for a short time, but the plaque comes back within hours. They do not replace brushing and cleaning between the teeth, and long daily use of strong ones is not advised unless a dentist recommends it.
Can germs in the mouth spread to other people?
Some bacteria, including those linked with decay, can pass through shared spoons or kissing, which is why parents are advised not to clean a baby's feeding spoon with their mouth. In adults this has little practical effect if the mouth is kept clean.
Can mouth bacteria affect the rest of the body?
Gum disease is associated with conditions such as diabetes and heart disease, and bacteria can enter the blood during dental infections. The links are associations rather than proven causes. Keeping the gums healthy is a sensible precaution.
About this page
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