Gum infections start with bacteria, but a range of factors determine whether those bacteria actually cause damage. About 42% of U.S. adults over 30 have some form of periodontal disease, and the causes go well beyond skipping the floss. Plaque buildup is the primary trigger, but your genetics, hormones, medications, and overall health all influence how vulnerable your gums are.
How Bacterial Plaque Triggers Infection
Every gum infection begins with plaque, the sticky film of bacteria that forms on your teeth throughout the day. These bacteria aren’t just sitting there passively. They organize into structured communities called biofilms, communicating with each other through chemical signals that coordinate their behavior. As the colony grows, bacteria release waste products that irritate the surrounding gum tissue.
Your immune system responds by sending white blood cells to the site to kill the invading bacteria, which causes the redness, swelling, and bleeding you recognize as inflamed gums. This early stage is gingivitis, and it’s reversible with better oral hygiene.
The problem is that these bacterial communities have evolved ways to fight back. They release chemicals that confuse your white blood cells, making the immune response less effective. White blood cells only live about three days. If they fail to destroy a bacterium in that window, they break apart, and the destructive enzymes they carried (meant to kill bacteria) spill into the surrounding tissue. Those enzymes then damage the very gum and bone tissue they were supposed to protect. This is how gingivitis progresses into periodontitis, where you start losing the bone and connective tissue that hold your teeth in place.
The Bacteria That Do the Most Damage
Your mouth hosts hundreds of bacterial species, but only a few are responsible for serious gum infections. The most destructive group includes three species that researchers call the “red complex.” Of these, one in particular stands out for its ability to hijack your immune system rather than simply evade it.
This keystone pathogen doesn’t just infect your gums directly. It shifts the balance of your entire oral microbiome, making the whole bacterial community more harmful. It invades gum cells, avoids being cleared by your immune system, and actually exploits the inflammatory response for its own survival. It produces enzymes that increase the permeability of tiny blood vessels in your gums, inhibit blood clotting, and increase bleeding. It also breaks down parts of your complement system, a key defense mechanism, which reduces bacterial elimination while ramping up inflammation.
The result is a cycle: your body mounts an immune response that the bacteria manipulate, leading to more tissue destruction, deeper pockets between your teeth and gums, and more space for bacteria to colonize.
Smoking and Gum Disease Risk
Smoking is one of the strongest modifiable risk factors for gum infections. A large meta-analysis found that smokers have an 85% higher risk of developing periodontitis compared to non-smokers. Tobacco reduces blood flow to the gums, impairs your immune response, and slows healing. It also masks early warning signs: smokers often have less visible bleeding, which can delay diagnosis even as the disease progresses underneath.
Diabetes Creates a Two-Way Problem
The relationship between diabetes and gum disease runs in both directions. People with poorly controlled blood sugar have two to three times the risk of developing periodontitis compared to those without diabetes. Chronic high blood sugar impairs immune function and blood vessel health, making gum tissue more vulnerable to bacterial attack and slower to heal.
But gum infections also make diabetes harder to manage. The chronic inflammation from periodontitis releases inflammatory molecules into the bloodstream that interfere with blood sugar regulation. Studies have shown that successful periodontal treatment reduces levels of key inflammatory markers in people with diabetes, which can improve glycemic control. If you have diabetes, gum health isn’t a separate concern from blood sugar management. They’re the same fight.
Hormonal Changes During Pregnancy
Pregnancy gingivitis is well documented, with both the prevalence and severity of gum inflammation increasing as pregnancy progresses. Rising levels of estrogen and progesterone are the main drivers. These hormones alter the composition of bacteria living below the gumline, shift the local immune response in gum tissue, and increase blood flow to the gums, making them more reactive to plaque that might not have caused problems before.
The good news is that maintaining thorough oral hygiene during pregnancy can partially offset the hormonal effect. The inflammation is initiated by plaque, and hormones amplify it. Reducing the plaque reduces the amplification.
Genetic Susceptibility
Some people are genetically predisposed to more aggressive gum disease. Research has identified specific gene variations that affect how your body produces inflammatory signaling proteins. In one landmark study of non-smokers, people who carried a particular combination of two gene variations had nearly seven times the risk of severe chronic periodontitis compared to those without them.
These genetic differences influence how strongly your immune system reacts to bacterial infection. A more aggressive inflammatory response sounds like it would be protective, but in gum tissue, excessive inflammation is what drives bone loss. If you’ve had persistent gum problems despite good oral hygiene, genetics may be part of the explanation. Multiple meta-analyses have confirmed that at least two specific genetic markers are associated with periodontal inflammation and can be used in risk assessment.
Medications That Change Your Gums
Certain medications cause gum overgrowth, a condition where gum tissue becomes thick and fibrotic, sometimes growing to partially cover the teeth. This makes it physically harder to clean effectively and creates sheltered pockets where bacteria thrive.
Three drug classes are the most common culprits:
- Anticonvulsants used for epilepsy, particularly phenytoin, which causes gum overgrowth in roughly 50% of adults who take it
- Immunosuppressants prescribed after organ transplants or for autoimmune conditions, with about 30% of patients on cyclosporine experiencing overgrowth
- Calcium channel blockers used for high blood pressure and heart conditions, with nifedipine affecting about 20% of users
These drugs alter how gum tissue cells function, leading to excessive tissue buildup. If you take any of these medications and notice your gums looking puffy or growing over your teeth, your dentist can help manage the issue, sometimes by coordinating with your prescribing doctor on alternative medications.
Vitamin C Deficiency and Gum Breakdown
Vitamin C is essential for producing collagen, the structural protein that holds your gum tissue together. When your body’s total vitamin C stores drop below about 350 mg (from a normal reserve of around 1,500 mg), clinical signs of deficiency appear. In the gums, this means fragile blood vessels, spontaneous bleeding, and impaired wound healing.
Severe deficiency, known as scurvy, is rare in developed countries but milder deficiencies are not. People with very restricted diets, chronic alcohol use, or conditions that impair nutrient absorption are most at risk. Even without full-blown scurvy, low vitamin C levels weaken the gum tissue’s ability to resist bacterial invasion and repair itself after inflammation.
Dry Mouth and Reduced Saliva
Saliva does more than keep your mouth comfortable. It continuously washes away food particles, neutralizes acids produced by bacteria, and contains antimicrobial proteins. When saliva production drops, whether from medications (antihistamines, antidepressants, and blood pressure drugs are common causes), medical treatments like radiation therapy, or conditions like Sjögren’s syndrome, bacteria accumulate faster and plaque builds up more easily. Chronic dry mouth significantly raises your risk of both tooth decay and gum infections.
Poor Oral Hygiene Ties It All Together
Every risk factor on this list interacts with plaque. Genetics load the gun, diabetes and smoking pull the trigger, hormones amplify the signal, but plaque is the ammunition. Without bacterial buildup along and below the gumline, gum infections don’t take hold. That’s why people with multiple risk factors benefit most from aggressive plaque control: thorough brushing, daily cleaning between teeth, and regular professional cleanings to remove hardened plaque (tarite) that can’t be removed at home.
The progression from healthy gums to gingivitis to periodontitis isn’t inevitable at any stage. Gingivitis reverses completely with improved hygiene. Even periodontitis can be stabilized, though lost bone doesn’t fully regenerate. The earlier you address the causes, the less damage accumulates.