Gum infections start with bacteria. A sticky film of bacteria called plaque builds up along and below the gumline every day, and when it isn’t removed through brushing and flossing, it triggers an inflammatory immune response in the surrounding tissue. About 42% of American adults over 30 have some form of periodontal disease, and it remains the most common cause of tooth loss in adults. Understanding what drives gum infections, from the bacterial basics to the less obvious systemic factors, can help you recognize and reduce your risk.
How Plaque Leads to Infection
Plaque is a biofilm, a structured colony of bacteria that forms on your teeth in a predictable sequence. First, early-arriving bacteria attach to the thin protein layer that coats your enamel within hours of brushing. Once anchored, these pioneer species create a scaffold that lets additional bacteria latch on. Within a day or two, the colony matures into a complex community with dozens of interacting species.
If plaque stays on your teeth long enough, it hardens into tarite (also called calculus), a rough deposit that sits right at or below the gumline. Tartar can’t be removed with a toothbrush. It gives bacteria a protected surface to keep multiplying and pushes deeper below the gumline, where your body’s immune cells respond with inflammation. That early inflammation is gingivitis: red, swollen gums that bleed easily. Gingivitis is reversible with better oral hygiene, but when it’s left untreated, the infection can progress into periodontitis, where the tissue and bone supporting your teeth begin to break down.
The Bacteria Behind the Damage
Not all mouth bacteria are harmful. Your oral microbiome contains hundreds of species, and most are harmless or even protective. Gum infections are driven by a smaller group of aggressive species that thrive in the low-oxygen environment of deep gum pockets. The most consistently identified culprits in chronic periodontitis include species that destroy tissue directly, produce toxins, or hijack the immune response to cause collateral damage to bone and connective tissue.
These harmful bacteria don’t usually dominate a healthy mouth. They gain a foothold when plaque is allowed to accumulate undisturbed, shifting the balance of the microbial community from mostly harmless to disease-causing. The deeper the pockets between your teeth and gums become, the more favorable the environment gets for these aggressive species, creating a cycle that accelerates tissue loss.
Smoking and Gum Infections
Smoking is one of the strongest risk factors for gum disease. It weakens your immune system’s ability to fight off infection in gum tissue and simultaneously slows healing once damage occurs. This double effect means smokers are more likely to develop periodontitis, more likely to have severe cases, and less likely to respond well to treatment. The reduced blood flow caused by nicotine also masks early warning signs: smokers often have less visible bleeding, which can make gingivitis harder to catch before it progresses.
Diabetes and Blood Sugar
Diabetes and gum disease have a two-way relationship. High blood sugar increases glucose levels in your saliva, which feeds the bacteria that form plaque. At the same time, poorly controlled diabetes impairs the immune response and slows tissue repair, making existing gum infections harder for your body to contain. According to the National Institute of Diabetes and Digestive and Kidney Diseases, high blood glucose levels increase the risk that mild gum disease will progress to severe periodontitis. Keeping blood sugar well managed directly reduces your risk.
Hormonal Changes
Shifts in estrogen and progesterone increase blood flow to the gums and make the tissue more sensitive to the bacteria already present in plaque. This is why gum infections flare during specific life stages. Pregnancy gingivitis is particularly common: rising hormone levels cause gums to swell, redden, and bleed more easily, even with a normal brushing routine. Puberty and menopause can trigger similar changes. The hormones don’t cause infection on their own, but they amplify the body’s inflammatory reaction to plaque that might not have caused problems before.
Medications That Affect Your Gums
Certain prescription drugs can cause gum overgrowth, a condition where gum tissue swells and grows over the teeth, creating deep pockets that trap bacteria and make cleaning nearly impossible. Three categories of medication are most commonly involved:
- Seizure medications: Phenytoin is the most well-known offender. Roughly half of the people who take it develop some degree of gum overgrowth. Other anticonvulsants, including carbamazepine and valproic acid, carry a lower but real risk.
- Blood pressure medications (calcium channel blockers): Nifedipine causes gum overgrowth in about 38% of users. Diltiazem follows at around 20%, with other drugs in the same class carrying lower rates.
- Immunosuppressants: Cyclosporine, used after organ transplants and for autoimmune conditions, causes gum overgrowth in an estimated 13% to 85% of patients depending on the study.
Other medications contribute indirectly. Drugs that cause dry mouth, including many antidepressants, antihistamines, and decongestants, reduce the saliva flow that normally washes bacteria off teeth and neutralizes acids. Less saliva means plaque accumulates faster.
Other Risk Factors
Poor nutrition weakens your body’s ability to fight infection everywhere, including your gums. Vitamin C deficiency in particular has a long-established link to gum disease, since the vitamin plays a direct role in maintaining connective tissue. Chronic stress raises levels of the stress hormone cortisol, which suppresses immune function and increases inflammation.
Genetics also play a role. Some people are simply more susceptible to aggressive gum disease despite good oral hygiene. If close family members lost teeth to gum disease, your risk is elevated. Clenching or grinding your teeth (bruxism) doesn’t cause infection directly, but the excess force can accelerate bone loss in gums that are already inflamed.
How Gum Infections Progress
Dentists measure gum health partly by checking the depth of the pocket between each tooth and the surrounding gum tissue, using a small probe. Healthy gums have pocket depths of 3 millimeters or less. At 4 millimeters, you’re in a gray zone between health and disease. Pockets of 5 millimeters or deeper signal active periodontal attachment loss, meaning the tissue and bone anchoring the tooth are being destroyed.
Gingivitis, the earliest stage, involves inflammation of the gum tissue only. Your gums may look puffy, feel tender, or bleed when you brush. No bone loss has occurred yet, and the condition is fully reversible. When gingivitis advances to periodontitis, the infection moves below the gumline. Your immune system’s prolonged inflammatory response starts breaking down the bone and fibers that hold teeth in place. Pockets deepen, teeth may loosen, and without treatment, tooth loss follows. About 7.8% of U.S. adults over 30 have severe periodontitis, while 34.4% have a milder form.
The progression from gingivitis to periodontitis isn’t inevitable. It depends on how long plaque remains undisturbed, how aggressive the bacterial species involved are, and how your individual immune system and risk factors interact. Some people develop severe disease quickly; others carry mild gingivitis for years without it worsening. Consistent plaque removal, whether through daily brushing, flossing, and professional cleanings, remains the most effective way to prevent bacteria from gaining the upper hand.