Diseased gums are easy to spot, they're red and they're inflamed. If yours are red around the area where your tooth meets the gum, if that area is sensitive to the touch, or if it bleeds when you brush or floss, you've most likely got some amount of gingivitis.
Here's how it happens:
Bleeding, sensitive gums are usually signs that plaque is hiding somewhere in the area, probably within the gum's pockets, that deepened furrow between the neck of the tooth and the gum. A pocket is a sulcus that's become too deep, and the deeper the space, the more difficult it is for both you and even your dental expert to reach. So, since cleaning it is impossible, plaque can pile up with no disturbances from a toothbrush, floss or any at-home tool. After a while, the plaque hardens, and it must be removed.
This plaque is a different kind of plaque from the one that de-mineralizes a tooth. This plaque is formed from anaerobic bacteria. When these bacteria accumulate around the gum area on the root surface, the gum becomes inflamed, sort of like a splinter that's lodged itself under skin. This is another example of an inflammatory response. And this is a crucial time. If you don't take care of this inflammation, you'll soon find yourself crossing over from gingivitis to the much darker world of periodontal disease and bone loss.