Gum infections develop when bacteria in your mouth build up along and below the gumline, triggering inflammation that can progress from mild gum swelling to serious tissue and bone damage. About 42% of U.S. adults aged 30 and older have some form of gum disease, making it one of the most common chronic infections in the country. The process is gradual, driven by a combination of daily habits, underlying health conditions, and your body’s own immune response.
How Bacteria Build Up on Your Teeth
Your mouth contains hundreds of bacterial species, most of them harmless. The trouble starts when these bacteria organize into a sticky, structured layer called a biofilm, commonly known as plaque. This happens in stages. First, a thin protein film coats your teeth within minutes of brushing. Bacteria then latch onto that film, initially with weak bonds that saliva could wash away. If they aren’t disturbed by brushing or flossing, the attachment becomes permanent.
Once anchored, the first wave of bacteria creates a scaffold that allows other species to pile on. The colony grows into a three-dimensional structure, and the bacterial makeup shifts. Early colonizers tend to be relatively benign, but as the biofilm matures, more aggressive species move in. These later arrivals thrive in the low-oxygen environment deep in the biofilm and produce toxins that irritate gum tissue. Pieces of the biofilm can also break off and resettle on other tooth surfaces, spreading the process around your mouth.
If plaque isn’t removed within about 48 to 72 hours, it begins to harden into tarite (calculus), which you can’t brush off at home. Tartar provides a rough surface that makes it even easier for new plaque to accumulate, accelerating the cycle.
From Plaque to Infection
Healthy gums fit tightly around each tooth, with a small gap (called a sulcus) measuring 1 to 3 millimeters deep. A toothbrush can reach bacteria within that range. When plaque builds up and inflames the gum tissue, though, that gap deepens into a pocket. Once a pocket reaches 4 millimeters or more, your toothbrush can no longer clean it, and bacteria multiply in a sheltered space your daily routine can’t touch.
The earliest stage of gum infection is gingivitis: red, swollen gums that bleed easily when you brush or floss. At this point, no bone or connective tissue has been destroyed, and the condition is fully reversible with better oral hygiene. If gingivitis goes untreated, it can progress to periodontitis, where the infection spreads below the gumline. Pocket depths of 5 to 7 millimeters indicate moderate periodontitis, and measurements of 7 to 12 millimeters signal advanced disease with significant bone loss.
No single bacterial species causes periodontitis. Instead, the infection results from a shift in the overall bacterial community. As inflammation increases, the mix of microbes changes: protective species decline while more harmful, oxygen-avoiding bacteria take over. This shift is self-reinforcing. Inflammation feeds the aggressive bacteria, which produce more toxins, which drive more inflammation.
Your Immune System Can Make It Worse
One of the most counterintuitive aspects of gum disease is that much of the tissue damage comes from your own immune system, not directly from bacteria. When your body detects the bacterial invasion below the gumline, it launches an inflammatory response. Immune cells flood the area and release signaling molecules meant to fight the infection. In a healthy scenario, this response clears the threat and subsides.
In periodontitis, the bacterial presence is constant, so the inflammatory response never shuts off. The same molecules your body uses to fight bacteria also break down the connective tissue holding your teeth in place and actively stimulate bone resorption. This creates a destructive feedback loop: tissue breakdown releases nutrients that feed the harmful bacteria, the bacterial community becomes more aggressive, and inflammation ramps up further. Over months and years, this cycle erodes the bone supporting your teeth.
Risk Factors That Set the Stage
Smoking
Smoking is one of the strongest risk factors for gum disease. It reduces blood flow to the gums, impairs immune cell function, and slows healing. A smoker with diabetes who is 45 or older is 20 times more likely to develop severe gum disease than someone without those risk factors. Smoking also masks early warning signs because reduced blood flow means your gums may not bleed as noticeably, even when infection is present.
Diabetes
Poorly controlled blood sugar weakens your body’s ability to fight infections of all kinds, including gum infections. High glucose levels in saliva also feed oral bacteria. The relationship goes both ways: gum disease makes blood sugar harder to control, and uncontrolled blood sugar makes gum disease worse.
Hormonal Changes
Pregnancy, puberty, and menopause all alter gum tissue sensitivity. During pregnancy, elevated levels of estrogen and progesterone increase blood flow to the gums and make capillaries more fragile, while simultaneously weakening the immune cells that normally keep plaque bacteria in check. The result is that even a small amount of plaque, the same amount that caused no problems before pregnancy, can trigger swollen, bleeding gums. This is common enough to have its own name: pregnancy gingivitis.
Certain Medications
Some medications change your gum tissue in ways that invite infection. Drugs used to prevent seizures (particularly phenytoin) cause gum overgrowth in an estimated 15 to 50% of people taking them. Immunosuppressants used after organ transplants cause similar overgrowth in about 27% of patients. Blood pressure medications in the calcium channel blocker class, such as amlodipine and nifedipine, trigger gum overgrowth in 10 to 20% of users. Overgrown gum tissue creates deep folds that are difficult to clean, trapping bacteria and increasing infection risk.
Medications that cause dry mouth are another concern. Saliva is your mouth’s natural defense system: it washes away food particles, neutralizes bacterial acids, and contains antimicrobial proteins. Hundreds of common medications, including antidepressants, antihistamines, and decongestants, reduce saliva production as a side effect, leaving your gums more vulnerable.
Genetics and Immune Conditions
Some people are genetically predisposed to a stronger inflammatory response, meaning their immune system overreacts to normal levels of plaque bacteria. Conditions that suppress the immune system, such as HIV or cancer treatment, also make gum infections more likely and harder to control.
Other Ways Gum Infections Start
While plaque buildup is the primary cause, gum infections can also develop from other routes. A cracked or chipped tooth can allow bacteria to reach the gum tissue directly. Poorly fitting dental restorations, like crowns or bridges with gaps, create spaces where bacteria accumulate. Food impaction, where food repeatedly gets wedged between teeth, causes localized irritation that can progress to infection.
The bacteria responsible for gum disease can also be transmitted between people through saliva. Kissing, sharing utensils, or sharing toothbrushes can introduce harmful bacterial strains into your mouth, particularly if the other person has an active gum infection. This doesn’t mean a single kiss causes periodontitis, but regular exposure can shift your oral bacterial community in an unfavorable direction, especially if your oral hygiene is inconsistent.
Why Gum Infections Often Go Unnoticed
Gum disease is sometimes called a “silent” condition because it can progress significantly before causing pain. The early signs are easy to dismiss: gums that bleed a little during brushing, slight redness, mild puffiness. Many people assume bleeding gums are normal. They are not. Healthy gums do not bleed from routine brushing or flossing.
Other signs that a gum infection may be developing include persistent bad breath that doesn’t improve with brushing, gums that appear to be pulling away from the teeth (making teeth look longer), teeth that feel slightly loose or shift position, and changes in how your bite feels when you chew. By the time pain or significant looseness appears, substantial bone loss has often already occurred, which is why the early, painless signs matter.