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I Was Recently Surprised To Discover That, Unlike Brushing, Flossing Has Not Been Clinically Proven To Prevent Periodontal Infections.

Got Gingivitis? Before you floss, read this!

I was recently surprised to discover that, unlike brushing, flossing has not been clinically proven to prevent periodontal infections.

One of the common causes of endocarditis, it turns out, is getting a thorough tooth cleaning in a dentists office. The sharp instruments penetrating below the gum line force bacteria into the bloodstream. In immune compromised people, the infection can get out of control.When I was a kid I used to floss every day just like my dentist advised. Then I went though medical school and learned about something called endocarditis, a bacterial infection of the heart valves, which develops in people whose immune systems are unable to eradicate the invading bacteria before they can burrow into the valvular tissue.

For me, this is not merely a theoretical issue. My brother, who had a compromised immune system from a bone marrow transplant while I was in medical school, nearly lost his life when he had his teeth cleaned prior to undergoing radiation treatment.

Even in the absence of obvious infection, bacteria in the bloodstream can trigger a subclinical immune system response that may lead to inflammation in the blood vessel walls where it can contribute to atherosclerosis and other diseases associated with aging.

Like dental cleaning, flossing also forces bacteria into the bloodstream.

After my brother’s experience I reconsidered my flossing habit. Flossing removes food, but it seemed to me that shoving a string between your teeth and randomly sliding it around was unlikely to remove bacteria one thousandth the size of the string. What I decided to do instead was to focus instead on brushing right after a meal to prevent bacteria from forming the kind of biofilm that could establish between my teeth and under the gum line. Some bacterial species divide as quickly as every twenty minutes, so that was my cut-off time.

Since then, for the past twenty three years, I floss when I’ve gotten something stuck between my teeth and otherwise I’ve avoided flossing and have not had any problems.

   HealThy Mouth Summit is FREE if you sign up this week!
HealThy Mouth Summit is FREE if you sign up this week!

In fact, I hadn’t even given my lack of flossing much thought until my good friend from Kauai, Will Revak, asked me to participate in his HealthyMouth Summit, which launches today and runs through this week. When Will sent me the invitation, I immediately thought of the flossing question and decided it would be a great excuse to educate myself.

I go into more detail during the summit interview, but here’s two conclusions you may find surprising:

  • There’s never been any compelling research showing that daily flossing promotes better oral health or reduces gingivitis.
  • Some research suggests that if you have gingivitis and you floss irregularly, you are forcing bad bacteria into your bloodstream. Daily flossing in this setting may be advantageous, interestingly enough.
  • Water swishing, a less aggressive means of removing interdental debris, may be an effecive alternative.

So what should you do?

Of course I’m not a dentist, so I am not going to advise anyone to spit out the idea of flossing altogether. If you floss regularly and that working for you, that speaks for itself. Besides, if you have something stuck in your teeth, flossing is the fastest way get it out of there. But it does seem prudent that if you don’t floss and are immune suppressed for any reason, to talk to your dentist about what he or she recommends to reduce the risk of introducing significant amounts of bacteria into your bloodstream.

I found these articles balancing the risks of flossing interesting. I’m sticking to the idea that more information is almost always a good thing and invite other oral health professionals to join the conversation.

Publications that I found compelling include:

Bacteraemia Due to Dental Flossing

“Effect of Intensified Caries Prevention on Approximal Caries in Adolescents with High Caries Risk”

“Comparison of irrigation to floss as an adjunct to tooth brushing: effect on bleeding, gingivitis, and supragingival plaque”


Dr. Cate

With over two decades of clinical experience and expertise in genetic and biochemical research, Dr. Cate can help you to reverse metabolic disease and reshape your body.

This Post Has 43 Comments

  1. I don’t get things stuck between my teeth that often (cuz there’s almost or maybe even entirely no space between almost all of my teeth and the ones next to them) and when I do I just use my nails to get it close to the side and than I pull it out, no flossing required.

  2. Brushing teeeth immediately after brushing is bad. THe reason is that when chewng your mouth releases chemicals that are super strong to aid in breaking down the food you just chewed. These chemicals eat at enamel so one brushing their teeth will be brushing chemicals all over mouth and hurting enamel. It is better to rinsie mouth with water and then listerine(or a natural mouth rinse if you prefer, peroxide, or cloves).

  3. Is it helpful or harmful to rinse with hydrogen peroxide? I have heard so many mixed opinions.

  4. This sounds gross, but it is part of my story of overcoming inflammation by a change in diet over the last 6 months. For many years, the little rack where I put my toothbrush would become yellow and slimy and disgusting after just a day or so. Six months ago, a very high C-reactive protein number (17) got my doctor’s and my attention, and I went on an anti-inflammation diet. I thought I ate healthy before, but seven days of food-diary entries and some education told me a different story. Dr. Kate’s books were a part of my education as I turned away from industrially processed oils and other industrial and processed foods to a whole-food, low-glycemic diet. Now I get as much nutrition as I can from what is available to me, including fresh eating-off-the-ground hen eggs and ‘underground’ raw milk. Since then, this goo in my toothbrush holder is gone, and my teeth feel clean. (I still clean that toothbrush rack, though, and I still brush my teeth.) This is just one of so many changes that have occurred for me (not the least of which is the loss of 20 pounds with no effort whatsoever and the regaining of my energy and sanity). The modern processed-food, industrial diet is killing people day by day. Keep up the good work, Dr. Kate. I learned a lot from your books. If you relocate again, come to the Ozarks. It’s clean livin’ in these hills!

  5. For the past 5 months, I’ve been following a simple dental hygiene system that is spelled out by New York state dentist Dr. Ellie Philips in her book and on her various websites. She describes it completely and for free on her websites, so it is not necessary to purchase anything to benefit from her program.

    One thing that Dr. Ellie promotes is NOT flossing — in fact, she was just interviewed by the BBC (British Broadcasting Corp) about her views on flossing. By chance, I saw the post about her BBC interview on her blog earlier today, and then I have visited your blog for the first time ever this evening and landed on this post about not flossing – a coincidence! [More about her interview:

    I happen to feel that for me, flossing at night is a good thing, because my teeth are very tightly packed together and a lot of food and stuff gets trapped between them. If I don’t floss, all that stuff just sits there and builds up, and that can’t be good.

    Otherwise, I follow most of Dr. Ellie’s advice, and I have been very pleased with the outcome so far – my teeth were sensitive for 20 years and I was a slave to Sensodyne, but from the first day of Dr. Ellie’s program, I have only noticed any sensitivity just twice in 5 months (versus about once a day when I was using Sensodyne). My teeth have lost a lot of their yellow staining (without any bleaching or abrasion), and they look and feel healthier than they have in 20 years.

    You can see the reviews for Dr. Ellie’s book on Amazon and so forth – it’s called _Kiss Your Dentist Goodbye_ (she doesn’t really mean that people should totally stop seeing their dentists).

    The great thing about Dr. Ellie is that she offers her protocol for free, she is helpful and honest on her blog(s), and she does her best to explain her hypotheses but is open about testing things and continuing to learn new information. I wrote her with a question last month and she responded by email within a week. I had also made a suggestion for organizing her blog(s) and she implemented it immediately, and thanked me for it. She seems to be a good, well-meaning person.

    I may not agree 100% with everything she believes, but her basic program has worked well for me and my teeth, and when I saw a dentist 2 weeks ago for the first time since I have started Ellie’s system, he could not fault anything I was doing.

    Here is a link to a brief overview of her basic program:

  6. Cate,

    Disappointed in this article — seems speculative and not well thought out. Proper flossing is about technique and regularity. The floss should be slid down and back up next to each tooth (thus, each crevasse requires two passes), not haphazardly shoved between the teeth. And regular flossing will stimulate and strengthen the gums such that pain, discomfort, and bleeding become a thing of the past and the gums develop a healthy pink hue. They can even begin to grow higher if recessed.

    I never really bothered with flossing until a year ago when a dental bill made me rethink my priorities and I added regular flossing to my regular brushing routine. Since then, my teeth stay cleaner, my breath fresher, and my gums have lessened their cold sensitivity I had had since childhood. Yes, all that from flossing. Pretty good technique to know.

  7. We use a tea of cloves and cinnamon. I keep it in the fridge so it is cold but if you just hold it in your mouth for a moment it will warm. Then swish for as long as you like. Don’t swallow although it won’t hurt you. The cloves will make your mouth a little numb for a few minutes but no longer. This depends on how strong you make the tea as well. Google it for more info. We love it and will never use normal mouthwash again.

  8. If one’s teeth are not perfectly straight and food gets stuck the only thing to do is floss.
    I’d also rather have a professional clean now and then and not walk around like a hippie, using only salt to clean and trying to do everything naturally. It’s quality over quantity.
    Something else might kill me off in the meantime apart from my gingivitis caused by overcleaning, and all that’ll be left will be lots of photos of me with stained-looking teeth! 😀
    A facial,maxillary surgeon who has performed 3 implants for me over the past 12 years also said that it can take only 20 minutes for bacteria to proliferate – he did however advocate flossing and said one should also frequently change one’s toothbrush and to use soft brushes not hard nylon ones which can cause tiny scratches to one’s gums. He also recommends a toothpaste which is called Paradontax which tastes weird at first but is very good at keeping the gums healthy. He taught me to use tiny interdental brushes and said occasionally I could dip them in Chlorhexidene oral gel which kills off bacteria.
    Here is a link which shows a study of the efficacy of using Chlorhexidene oral gel.

  9. Dr. Cate, I see that you stated that your brother had a compromised immune system from undergoing a bone marrow transplant and then was going to undergo radiation treatment, rather than having heart valve issues. But again, there should have been some kind of consult between the oncologist and the dentist or advisement from the oncologist. It is routine for all dental professionals before the start of any appt to ask a patient if there are any updates in their medical history since their last visit. I had a patient in my chair that showed up for her dental cleaning, but before I started, I asked about any updates/changes in her health. She informed me she was undergoing cancer treatments and that her oncologist had advised her that she cannot undergo any dental treatment that would cause bleeding at this time; I promptly rescheduled her appt. This should have been advised to your brother (or parents if he was a minor at the time). It is unfortunate that this was not the case for your family.

    1. The most important thing we, as health professionals can do, is exactly what you describe: Inform our patients. Keep up the good work!

  10. After reading the above comments, some from fellow dental professionals as well, I am surprised that there has been no mention of the fact that us dental professionals take a very important precaution with our patients to prevent bacterial endocarditis (BE); patients with heart valve issues, as well as those whom have have joint replacement surgery, are suseptible to BE and thus the protocol is to have these patients pre-medicate with a single dose of antibiotics prior to any dental treatment that may cause bleeding. This has been in practice for years. Dr. Cate, you did not mention when this incident happened with your brother, but in my opinion, there was some negligence on the part of your brother’s physician (because physicians are aware of the need for antibiotic pre-med prior to dental treatment when there is a heart valve issue) and negligence on the part of the dentist if this heart valve issue was reported on your brother’s health history form completed at the dental office.

    As for periodontal disease, as a hygienist, that works in a periodontal office to boot, I have seen a lot of periodontal disease. However, I have been hypothesizing that periodontal disease may possibly be an autoimmune disease. Yes, plaque and tartar (calculus) buildup on the teeth are a factor in the development of periodontal disease, but they are not a single, definitive cause. I have seen countless patients present with an extremely high amount of plaque and tartar on their teeth, some that have not had a dental cleaning in 10 years or more, yet these patients do not develop the deep gum pockets or exhibit much bone loss on x-rays that is characteristic with periodontal disease. I also have patients that have excellent homecare and present with very little buildup of any kind on their teeth, yet they have persistent inflammation, bleeding and gum pocketing that just will not heal.

    Periodontal disease is a multi-factorial disease encompassing not only how well one brushes/flosses, but systemic health factors, outside factors such as smoking history, genetic predisposition and the individual’s overall health and ability to fight off infection. I believe there is still much to learn about periodontal disease, but I also firmly believe that proper nutrition can do wonders to aid dental diseases.

    I blogged about my periodontal disease as a possible autoimmune disease hypothesis here:

    and here:

  11. Vicky,
    Thank you. I wish my dentist had a dental hygienist like you!
    At least I finally found a dental office that wasn’t trying to up-sell all kinds of cosmetic crap like veneers and whitening.

  12. There is a right way to floss and a wrong way to floss. If you snap the floss in between your teeth you are more than likely going to irritate your gums and maybe even suffer some gum recession. The same goes for brushing; there is a right way and a wrong way. And as far as I’m concerned, the smartest thing I ever did was switch from a regular tooth brush over to an electric toothbrush because the latter of the two only vibrates against the teeth, and gums, and thus does not irritate them as manual toothbrushes so often do.

  13. After going low carb, and using tones of C , K2 and cod liver oil, nobody needs dentist. No flossing, no toothbrushing no anything… Understand “tones” literally 🙂

    How do u think we survived until dentistry ?

  14. Stephanie,
    I am a dental hygienist, practicing 30 years, plus a big fan of Weston A. Price Foundation and of alternative medicine.
    On my website, I wrote an article called “The Truth About Toothpaste.” The bottom line – you don’t need it. It is NOT “soap.” It doesn’t “dissolve” plaque or loosen it. It contains an abrasive, has flavoring, and is a topical fluoride application if it’s a TP w/ fluoride.
    Plaque is sticky, like peanut butter on a knife. Proper tooth brushing removes it, as does floss. Using baking soda and/or salt is a wonderful abrasive if you need it, plus both of these will draw inflammation out of the gum tissues. Although water swishing does remove food debris, it does not remove sticky bacterial plaque.
    I so appreciate your post and your comments about diet and stress. Most of the people I talk to about balancing their hormones look at me like I grew a 3rd eye or something. Out-of-balance hormones, and especially when stress is involved, cause gums to be soggy and spongy, more prone to infection. I see it everyday.
    All the best health to you! – Vicky

  15. Because I have extremely crooked teeth (probably caused by excess sugar as a young child), I typically get stuff stuck between them, especially the upper left molars. It’s quite uncomfortable, so I floss every night — and clean out quite a bit of leftover food in the process. I don’t know for sure how that affects my overall health, but it certainly increases my comfort. Although I have what amounts to a mouthful of semi-rotten teeth with lots of fillings and other dental work, I quit having major dental problems in 1999, the year I went on a low-carb diet.

    Off topic: I see that I will get to meet you in person in May, since Jimmy’s blog lists you as an official speaker on the LC cruise. I look forward to it. If I may be so bold, would you be willing to do a short podcast with me?

  16. I really enjoyed Dr. Cate’s interview on the HealThy Mouth Summit. My question is: what is the difference between what happens to fermented food (say the fish left under the sink that will make the “best broth”) and the food left between your teeth being flossed out? Why is one good in your body and the other is bad?

    I have numerous food sensitivities and cannot tolerate fermented or fungal foods. I have to use probiotic supplements. That greatly saddens me.


    1. This is a great question. I will forward to Will Revak and if you don’t get to call in on Saturday for the live QA we will try to get this in for you.

    2. One difference is in bacteria types – fermented foods are usually not left like that, but are seeded with specific cultures.

      And in environment – fermenting sugars between ur teeth equals constant acid cover unlike what happens when you swallow stuff and wash your mouth with water.

  17. Recently I started taking vitamin K2 supplements. The plaque behind my teeth has disappeared. It was getting to the point that I was sure I needed to have my teeth cleaned.

    This is the second time this has happened so I am sure that I was low on K2.

  18. I have heard that excessive toothbrushing can erode tooth enamel. Also, the way I have been told to brush, with the bristles pointing into the gum margin, seems just as likely to cause some minor abrasion to the gums and resulting bacteremia with the mechanical action on the bacteria that live there being pushed into microabrasions.

    Flossing always seemed like a safer way to clean out the stuff that can lodge in between teeth. I usually get some kind of crud out from between my teeth with the floss that brushing beforehand has been unable to remove.

    Eating a very low sugar diet and avoiding sticky sweet foods go a long way towards preventing plaque buildup. Eating lots of bone broths, along with healthy fats, Vit A and D, helps restore healthy tooth enamel and connective tissue supporting the teeth. Don’t forget that saliva is antibacterial. I don’t think rushing to brush one’s teeth after eating is necessary.

  19. Thank you Cate. Articles like these are a blessing to the general public. We alone are responsible for our health, and should know of practical observations that are contrary to socially accepted guidelines. Medical professionals who don’t welcome these kinds of challenges to their understanding, stop us from moving forward and keep us stuck in this horrible deteriorating public health cycle. Stats should be kept for people who choose the mainstream manner vs people who don’t. But most who don’t are socially criticized (mainly by professionals) or don’t want to admit it. Then how can we truly learn what’s best for us and our children. Mothers are directly invested in the welfare of our children and should know about all options. We can see for ourselves what ‘works’ and what doesn’t. Modern mainsteam medical and dental guidelines have benefitted an unsustainable market much more productively than the quality of our lives. Even worse, they have created a generation of mothers who aren’t taught to rely on their own learned wisdom, but the biased knowledge of ‘others.’

  20. Dear Dr Cate,

    I am very disappointed in this post. Your opinion probably has a big impact on your readers and the laziness of this piece of writing really upsets me. It is very misleading. What happened to being evidence based?

    There is a *lot* of research that supports the benefit of flossing. It is true that it is difficult to do correctly, but brushes just don’t get everywhere. Barely two minutes of searching turned up these journal articles:

    Benefits of flossing plus brushing as opposed to brushing alone:

    And on bacteraemia:

    -ie flossing sporadically is the problem, not flossing full stop.

    Yes flossing can cause a *transient* bacteraemia, especially when there’s lots of plaque around due to a poor diet and not flossing regularly. Toothbrushing does exactly the same thing. Are you recommending we stop brushing too? Eating causes a bacteraemia too. Should we stop eating? Daily life causes bacteraemias.

    Your brother’s situation was unusual and not a good basis for advising the general population not to floss. The National Heart Foundation here most definitely advises people with prosthetic heart valves, who really have one of the highest risks of problems cause by a transient bacteraemia, to maintain excellent oral hygiene and floss regularly as a way to minimise the risk of a subacute bacterial endocarditis.

    Most individuals have a diet that is great for growing plaque. It is very sticky and rinsing with water etc will not remove it. Surely the possibility of a very tiny transient bacteraemia caused by flossing is outweighed but the consequences of periodontal disease: Periodontal disease is linked with poor diabetic control, and cardiovascular disease, among other things.

    Yes, I am a dentist.

    I could go on (and on) pulling further parts of this apart, but I better not

    P.S. for Kathryn: achey gums after flossing is either

    1. your technique

    2. (or most likely) that it’s not regular enough and you’re getting some localised inflammation when you do do it.

    3. or if there’s some calculus there it will keep doing this. It needs to be removed.

    1. Thank you for your professional input. I appreciate your concerns and would like to see more considered thought on the subject of bacteremia within both dental and medical communities.

      Your comment on laziness is a little unusual, given that failure to bring up this issue with our patients represents a kind of professional complacency, or laziness, in my view, that puts people at unnecessary risk. Much like the mercury issue, and I think it also deserves more attention than it currently gets.

      I was aware of the second article you cite, which is from 1980, and it’s conclusion: “The results showed that the patients who flossed daily developed no bacteremias but that patients who delayed flossing from 1 to 4 days developed bacteremias 86% of the time.”

      Even according to the article you cite, anything less than diligent daily flossing runs a very high risk of bacteremia, something worth considering. What’s more, those authors who have since commented on this 1980 article are not convinced that even the daily flossers are free of this risk, explaining that it’s likely that the reason they failed to find bacteria was that they waited too long to perform the necessary testing to detect transient bacteremia, whereas the study I cited performed the testing within 30 seconds.

      I strongly suspect that if medical and dental professionals made it a common practice to warn patients of the bacteremia issue then my brother’s physicians would have realized that what they were doing to him was downright dangerous, and he could have been spared the extreme suffering and near death experience. His physicians did not make the connection between the dental cleaning and the septicemia until my mother, not a medical professional, asked the question. His physician changed his protocol as a result.

      I am sure his case in not unique, as you also suggest. People in fragile health undergo dental cleaning all the time. If they die of a ruptured aortic aneurysm 1-2 months later after a smoldering septicemia weakens an already dilated blood vessel wall, I doubt anyone would make the connection particularly in this day and age when autopsies are rarely performed.

  21. The dirtiest thing most of us ever do is put a toothbrush in our mouths

    And there are numerous studies showing bacteraemia (also spelt bacteremia) after simple toothbrushing,

    I don’t know what the answer is. But thankfully most of these cases of toothbrushing bacteraemia don’t give us endocarditis. However it probably is a contributor to chronic systemic inflammation.

    “LEAKY GUT STARTS IN THE MOUTH” copyright Dr Ben L Balzer

    I suggest you wash your toothbrush in hot water before and after every brushing, and also consider using a toothpaste containing an antiseptic such as triclosan (e.g. Colgate Total) or else occasionally with your dentist’s approval, use chlorhexidine digluconate (which is purported to not cause the staining problems of chlorhexidine gluconate).

    I’m a GP doctor, not a dentist, please seek the advice of your dentist!

    1. Triclosan is a MAJOR problem. Take a minute to look it up. I do feel we need to keep our toothbrushes bacteria free between brushes, so the hot water plus soap might be something I do more often.

  22. After reading Weston Price’s book, I kind of gave up on flossing. I was never a regular flosser anyway, but it just seemed like my teeth always hurt worse after doing flossing, so I quit.

    One time, in order to prepare for othodontia, I had to take my daughter to a specialist to have a tooth pulled. When we went back for a check up on her healing, this dentist/specialist got in my face about my mothering skills because my daughter had not flossed her teeth. At the time, we were doing a total remodel on our home. We had no bathroom and were brushing our teeth outside with the hose. I told him we didn’t even have a mirror in the bathroom yet, let alone the water hooked up and he told me he wasn’t interested in hearing my excuses. I asked him if we were all done and when he told me yes, I told him, “I’m glad we won’t have to return here again because you are an [email protected]” And we got up and left.

    My daughter, BTW, is 17 now and has never had a cavity. Thanks, Dr. Cate for this post. I always thought flossing was kind of a waste and I always hated what it did to my bathroom mirrors!!

  23. I have always flossed because I “should” and have been told it’s necessary.
    Even as a kid, when I could get my mum to buy me floss, I’d do it. My mouth is full of fillings, and I had a period of time where my gums were in bad shape in my late 20s.
    This is starting to sound like “cholesterol is the cause of heart attacks” when 50% of people who have heart attacks have low/normal cholesterol. “Flossing will prevent gum disease and cavities” – apparently not! I’m am seriously thinking about this now. Thank you.

  24. Hi Cate,

    What do you think about tartar / calculus? Should one have it removed once it has build up?

    I have plenty along the gums on the back of my front teeth having not been to a dentist for 8 years now. I used to get gum infections / sore swollen gums on occasion, but had never had it since going lchf more than a year ago. According to wikipedia “the ‘hardened’ calculus formations are at the heart of periodontal disease and treatment.” My experience seems to suggest this may not be true. As I said, I have plenty calculus, yet my problems went away with a change in diet while the calculus remains.

    So now I’m left to wonder: should I remove it? I had been pondering for some time whether it may do more harm than good.

    1. Of course since I’m not a dentist I don’t hav alot of expertise on gum disease but it seems like a good idea to remove the hard ‘crud’ that could distort your gum line.

  25. Hi Dr. Cate,

    Interesting article… I imagine this is especially relevant to those of us with mitral valve prolapse? What do you think of oil pulling instead? It seems that coconut oil is very popular for this, and since it has antimicrobial properties, might it not also prevent infection?

    Also, do you think swishing with homemade whey would be a good way to attend to periodontal issues?


    A. Dru

  26. Of course, this can be a can of worms, but I know you already know about it, and therefore, hopefully your readers should too,
    If you haven’t already you should check out what Dr. Price’s take on his own profession and its practices were, maybe he would have some insight on common dental routines such as flossing and it’s effectiveness. Though I haven’t yet read Dr. Price’s book “Nutrition and Physical Degeneration”, so I don’t know for sure.

  27. My dental hygienist was shocked to find out that I do not use commercial toothpaste. I brush with water and sometimes salt or soda. I never have been able to tolerate toothpaste, it makes me gag even thinking about it.
    She had to admit that although she had to work harder to clean the ‘staining’ on my teeth, it was not causing any harm to my health, my gums are healthy and I do not get cavities.
    Eating real food and keeping my hormones balanced with a low sugar, grain free diet and exercise keeps my gums healthy. When my hormones are out of whack due to stress (and when I was pregnant) then my gums can become inflamed.

  28. I never floss and the dentist always makes me feel guilty…but I have no cavities and no problems whatsoever. I appreciate your insightful post. Dr. Cate, do you have any idea when your next book will be published? I am really looking forward to it.
    Thank you for all you do,

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