Gingivitis is caused by bacterial plaque building up along the gumline, but a surprisingly wide range of factors determine whether that plaque actually triggers inflammation. Nearly half of U.S. adults over 30 have some form of gum disease, and while poor oral hygiene is the most common driver, hormones, medications, chronic conditions, and even nutritional gaps all play a role.
Plaque Buildup Is the Primary Cause
Bacteria in your mouth constantly form a sticky film called plaque on your teeth. When plaque sits along the gumline for more than a day or two, the bacteria produce toxins that irritate gum tissue. Your immune system responds with inflammation: redness, swelling, and bleeding when you brush or floss. This is gingivitis in its earliest form.
If plaque isn’t removed, it hardens into tarite (also called calculus), a rough, calcite deposit that can’t be brushed away at home. Tartar creates new surfaces for more plaque to cling to and pushes the gum tissue away from the tooth, deepening the pockets where bacteria thrive. At this stage, only a professional cleaning can remove it. The good news is that gingivitis is fully reversible with consistent plaque removal before it progresses to periodontitis, where the bone supporting your teeth starts to break down.
Smoking and Tobacco Use
Smoking is one of the strongest risk factors for gum disease. It weakens your immune system’s ability to fight infections in the mouth, so the bacteria in plaque meet less resistance. At the same time, smoking reduces blood flow to the gums, which slows healing once damage begins. This creates a cycle: your gums are more vulnerable to infection and less able to recover from it. People who smoke are also less likely to respond well to gum treatment compared to nonsmokers.
Hormonal Changes
Shifts in estrogen and progesterone can make your gums react more aggressively to the same amount of plaque that wouldn’t have caused problems before. These hormones increase blood flow to gum tissue and change how sensitive your gums are to bacterial irritation, making them more prone to swelling and bleeding.
Pregnancy gingivitis is the most well-known example. The significant rise in both estrogen and progesterone during pregnancy can cause gums to become inflamed, sore, and prone to bleeding even with good brushing habits. Puberty triggers a similar hormonal surge. Menstrual cycles and menopause can also cause periodic gum sensitivity in some people, though the effect is usually milder.
Diabetes and High Blood Sugar
Diabetes makes gingivitis both more likely and harder to control. High blood sugar weakens white blood cells, which are your body’s primary defense against mouth infections. With a compromised immune response, the bacteria in plaque can cause more damage before your body fights back.
There’s a second mechanism at work too. When blood sugar is elevated, saliva also contains more sugar. The bacteria in plaque feed on that sugar, which accelerates plaque formation and gives those bacteria more fuel to produce the toxins that inflame your gums. People with poorly controlled diabetes often notice their gums bleed more frequently, and gum disease tends to progress faster than it does in people with normal blood sugar levels.
Certain Medications
Several common drug classes can cause the gums to physically overgrow, a condition called gingival hyperplasia. The swollen tissue creates deeper pockets around the teeth where plaque collects, setting the stage for chronic inflammation. Three main categories of medications are responsible:
- Anti-seizure medications: About half of patients taking phenytoin develop some degree of gum overgrowth. Other seizure medications, including carbamazepine and valproic acid, can have the same effect.
- Blood pressure medications (calcium channel blockers): Nifedipine carries the highest risk at roughly 38% of patients. Other drugs in this class carry lower but still notable risk, ranging from 3% to 20% depending on the specific medication.
- Immunosuppressants: Cyclosporine, commonly used after organ transplants, causes gum overgrowth in an estimated 13% to 85% of patients.
Overall, roughly 40% to 50% of people taking any of these drugs will develop some gum overgrowth. Medications that reduce saliva production (including certain antidepressants, antihistamines, and decongestants) can also increase gingivitis risk indirectly, because saliva helps wash bacteria off your teeth.
Vitamin C Deficiency
Vitamin C is essential for building and repairing connective tissue throughout your body, including the tissue that holds your teeth in place. Without enough of it, gums become swollen, spongy, and bleed easily. In severe cases, this progresses to scurvy, where gums turn purple and teeth can loosen or fall out.
Full-blown scurvy is rare in developed countries, but mild vitamin C deficiency is more common than most people realize, particularly in smokers (who burn through vitamin C faster), people with very restricted diets, and older adults with limited food variety. Even a moderate shortfall can make gum tissue slower to heal and more susceptible to bacterial damage.
Weakened Immune System
Any condition that suppresses immune function makes gingivitis more likely. HIV/AIDS is a well-documented example, as the loss of immune cells allows oral bacteria to flourish. People undergoing chemotherapy or taking long-term immunosuppressive drugs face similar risks.
Autoimmune conditions also have a surprising connection to gum health. Research from Johns Hopkins found that a specific bacterium involved in gum disease, called Aggregatibacter actinomycetemcomitans, can trigger the same kind of inflammatory immune response seen in rheumatoid arthritis. Nearly half of patients with rheumatoid arthritis showed evidence of infection with this bacterium, compared to just 11% of healthy individuals. The relationship appears to go both ways: gum disease may worsen autoimmune inflammation, and autoimmune conditions may make gums more vulnerable.
Other Contributing Factors
Genetics play a role that’s easy to overlook. Some people mount a stronger inflammatory response to the same amount of plaque, which means they develop gingivitis faster even with decent oral hygiene. If gum disease runs in your family, you may need to be more diligent about professional cleanings.
Stress increases levels of the hormone cortisol, which dampens immune function and makes it harder for your body to manage bacterial infections in the mouth. Poor nutrition beyond just vitamin C, particularly deficiencies in B vitamins and calcium, can weaken gum tissue. Mouth breathing, which dries out the gums, and poorly fitting dental restorations that trap plaque can also create conditions where gingivitis takes hold more easily.
Age is another factor. While gingivitis can develop at any age, the prevalence of gum disease increases significantly after 30. This reflects the cumulative effect of years of plaque exposure combined with the gradual changes in immune function and tissue healing that come with aging.