Chapter 21: The Sweet Exceptions — Licorice and Manuka Honey

I need to tell you about two remedies that seem to violate everything I've said about sugar and oral health. Both are sweet. Both have been used for healing since antiquity. And both, paradoxically, may actually protect teeth rather than harm them.

The key, as always, is in the chemistry.

Licorice Root (Glycyrrhiza glabra and G. uralensis)

Licorice is one of the most extensively documented medicinal plants in history. It appears in the Ebers Papyrus from ancient Egypt (circa 1550 BCE), in traditional Chinese medicine texts going back millennia, in Greek and Roman herbals, and in medieval European apothecaries.¹

The root has a distinctive sweet taste—it's actually sweeter than sugar, though the sweetness compounds are different molecules entirely.

The Chemistry

Glycyrrhizin (glycyrrhizic acid): The primary sweet compound, about 30-50 times sweeter than sucrose.² It's a triterpenoid saponin with significant biological activity—anti-inflammatory, antiviral, and hepatoprotective. This is also the compound that can cause problems with prolonged high-dose use (more on that below).

Glabridin: A flavonoid found specifically in G. glabra (European licorice) with strong antioxidant and antimicrobial properties.

Licoricidin and licorisoflavan A: These are the oral health superstars—isoflavonoids that specifically interfere with S. mutans and biofilm formation.³

Other flavonoids: Multiple compounds with various antioxidant and anti-inflammatory effects.

The Oral Health Story

Here's where it gets interesting. Researchers discovered that specific licorice compounds don't just kill oral bacteria—they prevent bacteria from sticking to teeth in the first place.

Anti-adhesion mechanism: Licoricidin and licorisoflavan A inhibit S. mutans' ability to adhere to tooth surfaces. Remember, adhesion is the first step in biofilm formation. If bacteria can't stick, they can't colonize, and they can't cause caries.

Biofilm disruption: These compounds also interfere with the sticky glucan matrix that S. mutans produces. Without the matrix, biofilm structure is compromised.

Direct antimicrobial effects: Licorice compounds are bactericidal against S. mutans and S. sobrinus (another cariogenic species), with studies showing 99.9% killing at modest concentrations.

The Evidence

Clinical studies: Several studies have examined licorice for oral health:

The lollipop studies: Yes, really. Researchers created sugar-free lollipops containing licorice root extract and tested them in children. The results showed significant reductions in S. mutans counts after just 10 days of twice-daily lollipop use. The effect persisted for weeks after the intervention ended.⁴

This might seem counterintuitive—a candy that prevents cavities?—but the licorice compounds provide protection that outweighs the minimal sugar exposure (especially in sugar-free formulations).

Mechanism validation: In vitro studies have confirmed the anti-adhesion and antibiofilm effects.

Traditional use: Licorice root has been chewed for oral health across multiple cultures, including as a traditional tooth-cleaning stick in some regions.

Evidence level: Moderate-strong. The mechanistic evidence is compelling; clinical trials are limited but positive.

The Glycyrrhizin Caveat

Before you start consuming licorice by the handful, I need to warn you: glycyrrhizin has significant effects on the body.

Glycyrrhizin inhibits an enzyme (11-β-hydroxysteroid dehydrogenase) that normally inactivates cortisol.⁵ The result is that cortisol activity increases, which can lead to:

• Hypertension (high blood pressure)
• Hypokalemia (low potassium)
• Edema (fluid retention)
• In severe cases, cardiac effects

This is a real concern with chronic, high-dose licorice consumption. There are case reports of serious adverse effects from licorice candy (real licorice, not the artificially flavored kind).

For oral health purposes:

• Topical application (rinses, chewing) is lower risk than ingestion
• The oral health benefits may be achievable with deglycyrrhizinated licorice (DGL), which has the glycyrrhizin removed
• Short-term, moderate use is generally safe for healthy people
• Avoid if you have hypertension, heart disease, or are taking certain medications (diuretics, heart medications)

Practical Use

Licorice root tea rinse: 1. Simmer 1 tablespoon dried licorice root in 1½ cups water for 15-20 minutes 2. Strain and cool to warm 3. Use as a rinse, swishing for 30-60 seconds 4. Do not use daily long-term; intermittent use is safer

Licorice root chewing: Dried licorice root sticks can be chewed like miswak. The fibrous root cleans mechanically while releasing the active compounds. Limit to occasional use.

Commercial products: Some oral care products now incorporate licorice extract. Look for those that specify the anti-adhesion compounds (licoricidin, glabridin) rather than just "licorice flavor."

Manuka Honey

Now we get truly paradoxical: honey as an oral health product.

Honey is primarily sugar—fructose and glucose. By all conventional logic, it should be cariogenic. Yet traditional medicine across cultures has used honey for wound healing, including oral wounds. And a specific type of honey—Manuka, from New Zealand—has antimicrobial properties that have been validated by modern research.

What Makes Manuka Special

Manuka honey comes from bees that pollinate the Manuka bush (Leptospermum scoparium), native to New Zealand. While all honey has some antimicrobial activity (due to high sugar concentration, low pH, and hydrogen peroxide production), Manuka has an additional factor.

Methylglyoxal (MGO): This is a reactive compound found at much higher concentrations in Manuka honey than in other honeys.⁶ MGO is directly antimicrobial—it modifies bacterial proteins and DNA, interfering with bacterial function.

UMF and MGO ratings: Manuka honey is graded for its antimicrobial activity:

• UMF (Unique Manuka Factor): A composite rating; UMF 10+ is considered "medical grade"
• MGO: Direct measurement of methylglyoxal content; MGO 250+ corresponds approximately to UMF 10+

Oral Health Applications

Wound healing: Manuka honey promotes wound healing through multiple mechanisms—it maintains a moist wound environment, has anti-inflammatory effects, and stimulates tissue regeneration. For oral wounds (surgical sites, ulcers, burns), this can accelerate healing.

Antimicrobial effects: Despite being sugar, Manuka honey has demonstrated activity against oral pathogens in laboratory studies, including S. mutans and P. gingivalis.

Biofilm effects: Some studies suggest Manuka honey can inhibit biofilm formation and disrupt existing biofilms.

The Paradox of Sweet Antimicrobial

How can something so sweet be antimicrobial? Several factors:

1. Sugar concentration is so high it's actually osmotically hostile to bacteria (similar to salt)
2. MGO provides direct antimicrobial activity independent of sugar
3. Low pH (honey is acidic) inhibits bacterial growth
4. Hydrogen peroxide is produced when honey is diluted

The cariogenic risk is reduced when:

• Honey is applied topically rather than consumed
• Application is to specific sites (wounds, gums) rather than bathing teeth in sugar
• The antimicrobial and healing effects may offset the sugar exposure

The Evidence

Wound healing: Manuka honey has strong evidence for wound healing, including several Cochrane reviews for burns and surgical wounds.⁷ It's used in medical-grade wound dressings.

Oral health specifically: Evidence is more limited:

• In vitro studies show activity against oral pathogens
• A few small clinical trials suggest benefits for gingivitis and plaque
• Traditional use supports application for mouth sores

Evidence level: Strong for wound healing; moderate for oral antimicrobial effects; limited clinical trial evidence for routine oral care.

Practical Use

For oral wounds (canker sores, post-surgical sites): 1. Apply a small amount of high-grade Manuka honey (UMF 15+ or MGO 500+) directly to the wound 2. Let it sit for several minutes 3. You can swallow afterward or rinse gently 4. Repeat 2-3 times daily until healed

For gingivitis: Some practitioners recommend applying Manuka honey to inflamed gums, letting it sit, then rinsing. The evidence is limited, and you're applying sugar to teeth, so I'd suggest caution and limiting to short-term therapeutic use rather than daily routine.

NOT recommended for general caries prevention: Despite the antimicrobial properties, honey is still predominantly sugar. I wouldn't use it as a regular oral hygiene product. Reserve it for specific therapeutic situations—wounds, ulcers, acute inflammation—where its healing properties outweigh concerns about sugar exposure.

Sourcing Concerns

Manuka honey is expensive and frequently adulterated or mislabeled. If you're buying it for therapeutic use:

• Look for UMF or MGO certification
• Buy from reputable sources
• Expect to pay significantly more than regular honey

Cheap "Manuka" honey may not actually have the therapeutic compounds you're seeking.

The Sweet Paradox

What these two remedies share is a lesson about biochemistry: sweetness doesn't automatically mean danger.

Sugar—specifically sucrose—is the primary dietary substrate for S. mutans and the driver of caries. But the sweet taste itself isn't the problem; the problem is that specific bacteria can ferment specific sugars into enamel-dissolving acids.

Glycyrrhizin and the other sweet compounds in licorice aren't fermented by oral bacteria. They don't feed S. mutans. Instead, they actively interfere with bacterial adhesion and biofilm formation.

Manuka honey's antimicrobial compounds work despite the sugar content, and for wound healing specifically, the benefits may outweigh the cariogenic risk.

This is why I keep emphasizing understanding rather than following rules blindly. "Sweet is bad for teeth" is a simplification. The real story is about bacterial metabolism, acid production, and the specific chemistry of what you're putting in your mouth.

Licorice isn't sucrose. Manuka isn't table sugar. The mouth knows the difference—and so should you.

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Further Reading

For a detailed monograph on licorice, see herbalist Richard Whelan's excellent reference:

• Licorice Root — Comprehensive profile including traditional uses, glycyrrhizin safety considerations, and therapeutic applications

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1. Liquorice — Wikipedia. Documents licorice use from ancient Egypt through Chinese, Greek, Roman, and medieval European traditions. ↩

2. Isbrucker, R. A., & Burdock, G. A. (2006). Risk and safety assessment on the consumption of Licorice root (Glycyrrhiza sp.), its extract and powder as a food ingredient. Regulatory Toxicology and Pharmacology, 46(3), 167-192. ↩

3. Hu, C. H., et al. (2006). A novel antibiofilm effect of a herbal extract (Glycyrrhiza glabra) on S. mutans biofilms. Caries Research, 40(5), 467-470. ↩

4. Peters, M. C., et al. (2010). Effects of a lollipop containing licorice root extract on Streptococcus mutans in school children: a pilot study. European Journal of Dentistry, 4(1), 55-58. ↩

5. Glycyrrhizin — Wikipedia. The mechanism of pseudoaldosteronism through 11-β-HSD inhibition is well characterized. ↩

6. Mavric, E., et al. (2008). Identification and quantification of methylglyoxal as the dominant antibacterial constituent of Manuka honey. Molecular Nutrition & Food Research, 52(4), 483-489. ↩

7. Jull, A. B., et al. (2015). Honey as a topical treatment for wounds. Cochrane Database of Systematic Reviews, (3). CD005083. ↩