Does Chlorophyll Help Bad Breath? What the Research Says

What causes bad breath?

A Cochrane review explains that bad breath (halitosis) is usually caused by too much bacteria or trapped food particles in the mouth, most commonly at the back of the tongue. Those bacteria release sulfur compounds with an unpleasant smell.

Mayo Clinic lists other common causes, including strong-smelling foods like garlic and onions, tobacco, dry mouth, poor oral hygiene and gum disease, as well as some infections and medical conditions (Mayo Clinic). Because most cases start in the mouth, the most effective fixes usually target the mouth too.

Chlorophyll vs. chlorophyllin: what’s the difference?

Chlorophyll is the pigment that makes plants and algae green. Natural chlorophyll is fat-soluble and fairly unstable, and animal studies suggest only about 1% to 3% of it is absorbed, according to the Linus Pauling Institute at Oregon State University.

Chlorophyllin, usually sodium copper chlorophyllin, is a semi-synthetic, water-soluble mixture made from chlorophyll. The institute notes that most over-the-counter “chlorophyll” supplements and liquid drops actually contain chlorophyllin, because it’s cheaper and more stable. Green algae such as chlorella are also marketed as chlorophyll sources.

Where the bad-breath claim comes from

In the 1940s and 1950s, doctors observed that chlorophyllin applied to foul-smelling wounds reduced odor. That led to its use by mouth as an “internal deodorant,” mainly for people with colostomies or incontinence. The same deodorizing reputation later carried over to breath products, and it’s the root of today’s chlorophyll-for-breath marketing.

What the research actually shows

The evidence behind chlorophyll as a breath freshener is weaker than its popularity suggests:

• Odor from the gut: early case reports suggested 100–200 mg a day of chlorophyllin reduced fecal odor in ostomy patients, but a placebo-controlled trial found 75 mg three times a day worked no better than placebo (Linus Pauling Institute).
• A rare odor disorder: one small study in people with trimethylaminuria, sometimes called “fish odor syndrome,” found chlorophyllin lowered levels of the odor-causing compound in urine.
• Bad breath specifically: we couldn’t find well-designed modern clinical trials showing that swallowing chlorophyll or chlorophyllin reduces bad breath. Columbia University’s health Q&A service also notes that no long-term or large-scale human studies have confirmed chlorophyll’s broader health claims.

To keep this in perspective, bad breath is hard to study. Even for mainstream approaches like tongue cleaning and mouthwash, a 2019 Cochrane review of 44 trials found only low- to very-low-certainty evidence, largely because the studies were small. The difference is that those approaches target the actual source, bacteria in the mouth, while the case for swallowed chlorophyll rests mainly on old reports about odors from the gut.

Bad-breath approaches compared

Is chlorophyll safe to take?

For most adults, it appears to be. The Linus Pauling Institute notes that no toxic effects have been attributed to chlorophyllin in more than 50 years of clinical use. Possible side effects include:

• Green discoloration of urine or stool
• Yellow or black discoloration of the tongue
• Occasional diarrhea

Chlorophyllin can also cause false-positive results on some stool tests for hidden blood, so mention it to your doctor before that kind of test. Because its safety hasn’t been studied in pregnancy or breastfeeding, the institute advises avoiding it during those times.