Flossing is a critical piece of a health oral care routine as it helps to remove plaque buildup before it hardens into tartar. However if you do not floss regularly, your gumline can become irritated and inflamed. When bacteria, tartar, and plaque collect along your gumline, your gums may start looking unhealthy and you may see blood when flossing. There are a variety of different reasons why this could happen, including Periodontal disease, hormonal changes, certain medical conditions, or flossing incorrectly.