Gum disease in adults starts with bacterial plaque, the sticky film that constantly forms on your teeth. About 42% of American adults aged 30 and older have some form of periodontal disease, making it one of the most common chronic conditions in the country. While plaque buildup is the universal trigger, a combination of immune response, lifestyle habits, hormones, genetics, and even certain medications determines who develops mild inflammation and who progresses to serious tissue and bone loss.
How Plaque Triggers Inflammation
Your mouth contains hundreds of bacterial species that naturally colonize tooth surfaces. When you brush and floss regularly, these bacteria stay in check. When plaque accumulates, especially along and below the gumline, your immune system responds by sending white blood cells called neutrophils through the gum tissue and into the crevice between teeth and gums. That immune response is what causes the redness, swelling, and bleeding you recognize as inflamed gums.
This is the paradox of gum disease: the damage comes largely from your own body’s defense system, not directly from the bacteria themselves. Inflammation is supposed to tamp down the bacterial buildup, but when plaque isn’t removed, the immune response becomes chronic. Over time, it breaks down the very tissue it’s trying to protect.
The Bacteria That Do the Most Damage
Not all mouth bacteria are equally harmful. Three species in particular tend to cluster together in the pockets below the gumline and are strongly associated with the progression from mild gum inflammation to serious periodontal disease. Researchers grouped them as “red complex” bacteria in 1998 because they were consistently found together in patients with advanced disease. These bacteria thrive in the low-oxygen environment of deep gum pockets, and their presence signals a shift from a balanced oral microbiome to one that’s actively destructive.
In a healthy mouth, the bacterial community is diverse and relatively stable. As gum disease progresses, these aggressive species crowd out the beneficial bacteria and create an environment that feeds further inflammation. This is why gum disease tends to accelerate once it takes hold: the worse the infection gets, the better the conditions become for the bacteria driving it.
From Gingivitis to Periodontitis
Gum disease has two distinct stages, and the difference between them matters. Gingivitis is inflammation of the gum tissue without any loss of the bone or connective tissue holding your teeth in place. Your gums may bleed when you brush, look puffy, or appear redder than usual. The space between your gums and teeth (the pocket) typically measures 1 to 3 millimeters, and sometimes slightly more when swelling pushes the gum away from the tooth. The critical thing about gingivitis is that it’s fully reversible. Improved brushing, flossing, and professional cleaning can resolve it completely.
Periodontitis is what happens when gingivitis goes untreated and inflammation starts destroying the bone and connective fibers that anchor teeth. At this stage, the bone crest pulls away from the tooth, pockets deepen, and the damage can’t be undone on its own. Clinicians stage periodontitis by how much bone has been lost relative to the tooth root: early disease involves less than 15% of root length, moderate disease reaches up to a third, and advanced disease extends beyond the midpoint of the root. Of the 42% of adults with periodontitis, about 34% have mild or moderate forms, while roughly 8% have severe disease.
Smoking and Immune Suppression
Tobacco use is one of the strongest modifiable risk factors for gum disease. Smoking weakens your immune system’s ability to fight off the bacterial infection in your gums, and once damage occurs, it slows the healing process. This creates a double problem: smokers are more likely to develop gum disease and less likely to respond well to treatment.
Tobacco also reduces blood flow to the gums, which masks early warning signs. Smokers often experience less visible bleeding during gingivitis, which means they may not realize anything is wrong until the disease has progressed significantly. If you smoke and your gums don’t bleed when you brush, that’s not necessarily a sign of health. It may mean reduced circulation is hiding inflammation that’s already underway.
Hormonal Shifts Throughout Life
Fluctuations in estrogen and progesterone directly affect gum tissue. Higher levels of these hormones increase blood flow to the gums, making them more sensitive and more reactive to even small amounts of plaque. This is why gum problems often flare during puberty, menstruation, pregnancy, and menopause.
Pregnancy gingivitis is particularly common. The hormonal surge during pregnancy can make gums swell, bleed, and become tender even in women who previously had no gum issues. This doesn’t mean pregnancy causes permanent damage, but it does mean that the same amount of plaque that caused no symptoms before can suddenly trigger noticeable inflammation. Menopausal women may experience dry mouth and changes in gum tissue that also raise susceptibility.
Medications That Cause Gum Overgrowth
Certain prescription drugs cause the gums to grow over the teeth, a condition called gingival overgrowth. This overgrowth creates deep pockets where bacteria can hide and makes daily cleaning much harder, setting the stage for gum disease. Three categories of medication are the primary culprits: anti-seizure drugs, blood pressure medications (calcium channel blockers), and immunosuppressants used after organ transplants.
Roughly 40 to 50% of patients taking drugs in these categories develop some degree of gum overgrowth. Among people taking the anti-seizure medication phenytoin, about half are affected. For the blood pressure drug nifedipine, the rate is around 38%, while other calcium channel blockers like diltiazem (20%) and amlodipine (3%) carry lower but still notable risk. If you’re on any of these medications and notice your gums growing over your teeth, your dentist can work with your prescribing doctor to explore alternatives or manage the overgrowth before it leads to deeper problems.
Genetics and Individual Susceptibility
Some people seem to get gum disease despite good oral hygiene, while others with mediocre habits keep healthy gums for decades. Genetics plays a role in this variation. Researchers have identified specific gene variants linked to increased susceptibility, including variations in genes that regulate the inflammatory response. Certain variations in genes related to a key inflammatory signaling molecule have been associated with greater vulnerability to aggressive forms of periodontitis, though the connection varies across ethnic populations.
That said, genetic testing for gum disease risk isn’t yet reliable enough for routine use. Multiple large-scale analyses have found that the associations between specific gene variants and periodontal disease are inconsistent across populations and offer only modest predictive value. Genetics loads the gun, but plaque, smoking, and other environmental factors pull the trigger. Having a family history of gum disease is worth mentioning to your dentist, but it’s not destiny.
Vitamin C and Tissue Integrity
Vitamin C is essential for producing collagen, and collagen makes up roughly 60% of the structural tissue that holds your teeth in place. When vitamin C levels drop significantly, the body can’t maintain or repair these collagen fibers, leading to fragile blood vessels, swollen gums, and easy bleeding. Severe deficiency (scurvy) causes dramatic gum breakdown, but even moderate deficiency may worsen existing periodontal disease.
Studies have found that people with periodontal disease tend to have lower systemic levels of vitamin C compared to those with healthy gums. This doesn’t necessarily mean low vitamin C caused their gum disease, since plaque and bacteria remain the primary drivers. But because vitamin C is critical for collagen formation and tissue repair, inadequate intake likely makes it harder for gums to recover from the daily assault of bacterial inflammation. Most adults get enough vitamin C through a normal diet that includes fruits and vegetables, but those with very restricted diets or certain medical conditions may fall short.
Other Contributing Factors
Diabetes significantly raises gum disease risk. Poorly controlled blood sugar impairs immune function and slows healing, creating the same kind of vulnerability that smoking does. The relationship runs both ways: gum disease can make blood sugar harder to control, and high blood sugar feeds gum disease.
Chronic stress, poor sleep, and conditions that cause dry mouth also contribute. Saliva is one of your mouth’s primary defenses against bacterial buildup. Anything that reduces saliva flow, whether it’s a medication side effect, mouth breathing, or an autoimmune condition, gives plaque bacteria a significant advantage. Grinding or clenching your teeth adds mechanical stress to already-inflamed tissue, potentially accelerating bone loss in areas where periodontal disease is active.