When you first use an interdental brush it is normal to see blood in your saliva for the first few days. This should stop after about a week. If you have gum disease your gums can become inflamed and swollen and can bleed easily. Flossing and brushing alone are ineffective against gingivitis, the only effective way of getting rid of that is removing plaque. Interdental brushes may be sore and hurt a little when you first begin using them, but you will start to reap the benefits of pink, firm and healthy gums if you continue to use them.