Gingivitis is primarily caused by:

Gingivitis is primarily caused by the overgrowth of normal anaerobic biota, particularly certain species of bacteria that thrive in low-oxygen environments. These bacteria are part of the normal flora in the mouth but can become problematic when there is poor oral hygiene or build-up of dental plaque. These anaerobic bacteria produce toxins and metabolites that can irritate the gum tissue, leading to inflammation, redness, swelling, and bleeding gums, which are characteristic symptoms of gingivitis.

When individuals do not maintain proper oral hygiene, these anaerobic organisms multiply unchecked, causing an imbalance in the microbial community. This disruption is what ultimately leads to the condition known as gingivitis. In contrast, normal aerobic biota typically do not lead to this condition. Viral infections and excessive brushing can contribute to oral health issues, but they are not the primary causes of gingivitis.