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Why Gums Bleed When Flossing (And What To Do About It)

Gums have lots of small blood vessels going to them to keep them healthy. When these are damaged, you will see bleeding gums when you floss.

When I talk to my patients about flossing, one of their main concerns is that their gums bleed when flossing. Often they stop flossing because of it.

Many people suffer from bleeding gums. It is not normal or healthy. 

But it is common, especially when flossing.

Here I will talk about what causes gums to bleed during flossing and what you can do about it.

It’s worth noting that some people suffer bleeding gums simply when brushing their teeth, and the reasons for this are closely related to those that I outline below.

What are the reasons that gums bleed during or after flossing? 

Person pulling lip down to show bleeding gums
Image Source: Tsawwassen Place Dental Clinic

Gum disease is the most common reason that gums bleed when flossing

The most common reason for gums to bleed is because you have some form of gum disease. There are a few different causes of gingivitis (inflammation of the gums).

Gum disease is a collection of conditions affecting the gums. It is normally caused by bacteria in plaque. 

Flossing will lead to bleeding in gums if there is gum disease because of an increased blood flow to the inflamed gums.

Plaque induced gingivitis (gum disease)

Plaque induced gum disease occurs because of the collection of plaque on your teeth and gums.

When the plaque is not removed quickly enough, or well enough, the bacteria irritate the gums causing swelling or inflammation.

The initial phase is gingivitis and affects only the soft pink gum area. Left untreated, it will progress into the bone that supports the teeth. The result is periodontitis, characterised by the bone loss around the teeth.

At the initial phase of inflammation, your body responds by increasing blood flow to remove the bacteria.

This means that your gums are more likely to bleed when they are touched, such as by brushing or by flossing.

It is important that you remove the plaque from your teeth and gums. You do this by brushing and flossing.

Acute Necrotising Gingivitis

Acute Necrotising Gingivitis, sometimes referred to as AUG or ANUG, is a severe and specific infection of the gums.

This is less common than plaque induced gingivitis.

If you have this infection your gums will be very sore, with lots of ulcers, and with very bad breath too. It’s more common in younger males and smokers.

Your gums will definitely bleed when flossing if you have acute necrotising gingivitis, and you should visit the dentist if you think you have this condition.

Loose fillings can irritate gums and cause bleeding

Loose fillings can cause your gums to bleed when flossing. The loose filling can cause plaque induced gingivitis but can also traumatise the gum

This may be the cause if you notice that only one specific area bleeds when you floss. Also consider this possibility if you have been flossing for a while without any problem, and then your gums start bleeding.

The tooth next to this area may also be sore or sensitive when flossing, eating, or drinking.

Loose fillings will collect plaque and cause gum disease in the area next to where the filling has come loose. This process is then the same as for plaque induced gingivitis, where the increased blood flow means you are more susceptible to bleeding.

Another reason a loose filling can cause your gums to bleed when flossing is because the filling material itself rubs and irritates the gum itself. This leads to a small amount of bleeding if it is then irritated by flossing.

Incorrect Flossing Technique 

Person using dental floss

Sadly, using the wrong flossing technique can do some damage to your gums and lead them to bleed when you do floss.

This is a common concern I hear from patients who are new to flossing. They are worried that they are damaging the gums by flossing too hard.

If you scrub too hard or floss incorrectly, you can cause damage to your gums. 

Some people also find that using the wrong equipment can make things worse. Floss comes in different shapes and sizes, and selecting the best one for you will help with your technique.

Overall, it is unlikely that you are flossing too hard and damaging the gums. But if you are concerned, do get your technique checked by a dental professional.

Vitamin Deficiencies 

A lack of Vitamin C can cause connective tissues and capillaries to weaken. 

Studies have shown links between a deficiency and periodontal disease. Anything causing periodontal disease can cause gums to bleed when flossing.

This should be considered if your gums suddenly start bleeding even though you regularly floss, or if bleeding still occurs after you have been flossing for a few weeks or more.

Hormonal Changes

Changes in hormones can increase your susceptibility to bleeding gums. It can be such a small change that you only notice it when flossing.

Even subtle changes to hormones may cause your gums to start bleeding when flossing, even if it hasn’t happened before.

Reasons for changes in hormones include puberty, menstruation, pregnancy and menopause, with each one affecting you at different ages.

Keep your gums as clean as possible as they should settle down within a couple of weeks. 


Some medications can lead to bleeding as they cause gums to grow excessively. Other medications increase bleeding as they are designed to thin the blood.

If you are on these medications you may notice bleeding when flossing whether you are a regular flosser or not.

The most common medications that can lead to bleeding gums include:

  • Anticoagulants e.g. warfarin or heparin. These thin the blood and increase bleeding.
  • calcium channel blockers. These cause overgrowths on the gums which are susceptible to trauma.
  • Anticonvulsants e.g. phenytoin. These cause overgrowths on the gums which are susceptible to trauma.
  • Immunosuppressants e.g. cyclosporin. These cause overgrowths on the gums which are susceptible to trauma. They also affect your body’s ability to react to infection and are associated with severe periodontal disease.

Stopping Smoking

Smoking severely damages the blood vessels in your gums. 

When you quit smoking, the body repairs this damage and you get growth of new blood vessels. 

They are delicate when first forming, and are likely to bleed when flossing, although this will resolve with time.

What to do if you gums bleed when flossing

If you are flossing and have noticed that your gums are bleeding here’s a few things you can do:

  1. Stick with it! The most common cause is gum disease, which you can only cure by good cleaning. Bleeding gums are a common first reaction to starting a new flossing habit, so keep going with it. You should notice improvements within 7 days, and almost all bleeding should resolve within a couple of weeks.
  2. Improve your brushing technique. The better you can get rid of the plaque and bacteria, the sooner your bleeding gums will resolve. Don’t neglect your brushing. Use a proper technique to brush twice a day for two minutes.
  3. Check your flossing technique. Whilst it is normal for your gums to bleed when you first start flossing, do make sure you have the best technique. If you aren’t getting on with floss, consider another form of interdental cleaning, such as interdental brushes or a water flosser.
  4. See a dental professional if you are worried.

Dr. Chhaya Chauhan runs through the above in our video on getting started with flossing:

Flossing: A Quick Guide To Getting Started

Should you stop flossing if your gums bleed? 

No, do not stop flossing if your gums bleed.

If you are new to flossing and notice bleeding when flossing, you should not be concerned.

The gums are most likely bleeding because you have plaque induced gingivitis.

Keep going with daily flossing, or the schedule recommended by your dental professional and the bleeding should improve within 7 days. If they continue to bleed a lot after a couple of weeks of daily flossing, seek professional advice.

If you are a regular flosser and your gums have started bleeding suddenly, continue to keep flossing and seek professional advice. 

Do not stop flossing as this will lead to a buildup of plaque which can make gum conditions worse.

The exception to this is if your gums are so sore that you simply cannot touch them. In this case, see a dental professional as soon as you can.

Should I see a dentist if my gums bleed when flossing?

If you are new to flossing and your gums are bleeding, you should see a dental professional if it doesn’t stop bleeding within two weeks. 

Other reasons to see a dentist:

  • You have something stuck in your gums that you cannot remove at home.
  • You think you have a loose filling.
  • When you have been flossing for a while and then gums start bleeding suddenly.

About Dr. Gemma Wheeler, BDS (Hons)

Gemma qualified from Cardiff University School of Dentistry in 2015. She went on to complete her Foundation Training and a further two years in the Armed Forces, primarily based around Wiltshire. She now works in a private practice in Plymouth.

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