Floss before or after brushing? The right order, explained

Interdental plaque is the film that sits between two teeth, where bristles can't reach. It's the whole reason floss exists, so it's the right place to start the comparison.

The best-known test of sequence is a randomized crossover trial of 25 dental students (J Periodontol, 2018). Each person tried both orders, two weeks apart, after 48 hours without any oral hygiene. Flossing then brushing removed significantly more interdental plaque than brushing then flossing (p = 0.001), and more whole-mouth plaque as well (p = 0.009). Plaque right at the gum margin didn't differ between the orders.

The likely reason is mechanical. Floss loosens the debris between your teeth, and the brush and toothpaste that follow sweep it out. Do it the other way around and the loosened material sits there until your next brush. One small trial of dental students can't prove that story for everyone, but it's the clearest signal we have, and it points at floss first.

Fluoride only protects a surface it can reach. The same 2018 trial measured fluoride concentration in interdental plaque and found it significantly higher after the floss-first sequence (p = 0.027) (J Periodontol, 2018).

That's a sensible result. Plaque that's already been thinned out lets the fluoride in your toothpaste get closer to enamel. Brushing twice a day with fluoride toothpaste is what the CDC and the ADA recommend, so anything that helps it reach the tightest spaces is worth having.

Brush First isn't a disaster here. A separate crossover study found that flossing right after brushing barely changed salivary fluoride, and a fluoride mouthwash used after that raised it (Caries Res, 2009). So brushing first doesn't strip fluoride off your teeth. Flossing first just gives the fluoride a better path in.

Here's where the scoreboard flattens. A 2022 systematic review pooled the trials that compared the two orders and found no statistical difference in plaque index, the standard score for how much of the tooth surface plaque covers (Int J Dent Hyg, 2022).

The review covered only two trials and 60 patients, which is thin, and its authors said more studies were needed. It's still a reminder that one trial's edge didn't show up once the results were combined.

A 2026 randomized trial of 54 students backs that up. After 21 days, flossing before, after, or in the middle of brushing made no significant difference to plaque (p = 0.93) (BMC Oral Health, 2026). Over weeks, consistency washes out the sequence. That's the real headline, and it's why the verdict above is a lean rather than a win.

Gums that bleed when you brush or floss are a sign of gingivitis, the mildest form of gum disease (CDC). Bleeding is a better test of a routine than plaque, because plaque is what you remove and bleeding is what you're trying to prevent.

In the 2026 trial, Floss First and Brush First finished close together on the bleeding index at day 21, 0.75 against 0.70, with no difference between them reported. The group that flossed in the middle of brushing scored 0.52, significantly lower than Brush First (p = 0.012), which the authors flagged as worth more study (BMC Oral Health, 2026). Three weeks on students with healthy gums is too short and too small to change what the ADA tells you, so treat the mid-brush result as interesting, not as advice.

What should change your routine is bleeding that doesn't stop. Flossing shouldn't hurt, and gums that still bleed after a couple of weeks of daily cleaning deserve a dental visit. The CDC estimates that 42% of adults 30 and older have periodontitis, the more serious stage, and says a checkup at least yearly is how gum disease gets caught early (CDC).

The ADA's position is short. It recommends brushing twice a day and cleaning between your teeth once a day, and on sequence it says either way is acceptable as long as the cleaning is thorough (ADA).

Its consumer site puts it the same way: as long as you floss thoroughly, it doesn't matter when you do it, and the most important thing is to make flossing a daily habit (MouthHealthy).

That's consistent with the research. The big win in the evidence isn't the order, it's the floss. A Cochrane review of 35 trials found that flossing or using interdental brushes alongside brushing may reduce gingivitis, with low-certainty evidence (Cochrane, 2019). Low certainty isn't nothing. It's what you get when every trial is short and nobody can be blinded to whether they flossed. If you want technique, Feno's post on reusing a floss pick covers the part most people get wrong.

Mouthwash before or after brushing is a different question, and it has a clearer answer. The ADA says the before-or-after choice may come down to personal preference, with one caveat: ingredients interact, so manufacturers may recommend a specific order (ADA).

The interaction that matters most is fluoride. In a supervised crossover study, adults brushed with fluoride toothpaste and then rinsed with water, a fluoride mouthwash, or a non-fluoride mouthwash. The non-fluoride rinse roughly halved the fluoride retained in saliva over the next two hours. The fluoride rinse didn't (Caries Res, 2009). Rinsing with plain water after brushing lowers salivary fluoride too (BMC Oral Health, 2022), which is the whole case behind spit, don't rinse.

So the order is brush, spit, no water. If you want mouthwash, make it a fluoride rinse right then, or use any rinse at a different time of day. Cosmetic rinses only mask bad breath. Therapeutic rinses with fluoride, essential oils, or cetylpyridinium chloride do more, and none of them replace brushing and flossing (ADA). Children under 6 shouldn't use mouthwash unless a dentist says so. Feno's post on why mouthwash isn't enough goes deeper on that.

One honest footnote. If you brush with a fluoride-free paste such as Feno Foam, there's no toothpaste fluoride for a rinse to wash away, so the timing point above is about the paste you use. The ADA and the CDC recommend fluoride toothpaste for cavity prevention, and Feno's own guidance is to keep your fluoride rinse or whatever your dentist prescribes alongside the Foam.