The gingiva is your gums. Having "-itis" at the end of a word means inflammation. Gingivitis is when your gums become red, swollen, and bleed easily. Gingivitis that isn't treated can cause serious tooth and gum problems such as periodontitis.
Almost all gingivitis is caused by plaque. Plaque is a sticky film full of germs that builds up on your teeth. The most common cause of too much plaque is:
Plaque that stays on your teeth for more than a few days becomes hard. Hard plaque is called tartar. You can't remove tartar completely by brushing and flossing.
You can also get gingivitis from:
Taking certain medicines
Not getting enough vitamin C or niacin
Hormonal changes (for example, because of pregnancy or menopause)
Having an infection in your mouth
An impacted tooth (a tooth that hasn’t fully broken through your gum)