There are many causes of swollen and inflamed gums:
Gingivitis or periodontitis
Gingivitis is the most common cause of swollen gums. If plaque builds up on your gum line and teeth, over time it can become tartar (hardened plaque), which may lead to gingivitis. If left untreated, gingivitis can turn into a more serious infection called periodontal diseases (gum disease).1
Food particles and plaque also can get trapped under your gum line and cause an infection or gingivitis.2
Pregnancy
Pregnancy can cause significant changes in hormone levels. These changes may increase blood flow to the gums, making them more sensitive to swelling.3 Hormonal changes also can weaken the body’s ability to fight bacteria that cause gingivitis.4
Infection
Oral infections caused by fungi and viruses can cause swollen gums. Complications from infected teeth, such as a tooth abscess, may also lead to swelling near the tooth.6
Brushing and flossing too hard
Extra pressure doesn’t make your teeth and gums cleaner—it just makes your gums sore. When brushing, use soft, circular motions. When flossing, gently slide the floss up and down each tooth following the curve.7