Manuka Honey and the MGO / UMF Rating System

Table of Contents

1. Where Manuka Comes From: Leptospermum scoparium
2. The DHA-to-MGO Conversion in the Honey Jar
3. Mechanism: How MGO Kills Bacteria
4. The Three Rating Systems (MGO, UMF, NPA)
5. The New Zealand MPI Scientific Definition
6. MGO Strengths Used for Different Applications
7. Fraud and Watered-Down Manuka
8. Australian vs New Zealand Manuka
9. Cautions
10. Key Research Papers
11. Connections
12. Featured Videos

Where Manuka Comes From: Leptospermum scoparium

Manuka honey is the product of European honey bees (Apis mellifera) foraging on the nectar of Leptospermum scoparium, a small flowering shrub in the Myrtaceae family native to New Zealand and southeastern Australia. The plant is known as manuka or tea tree (not to be confused with Melaleuca alternifolia, the Australian tea tree from which tea tree oil is extracted). It grows abundantly on hillsides, in regenerating clearcut forest, and in scrub margins across both islands of New Zealand and parts of Tasmania, Victoria, and New South Wales.

The flowering window is narrow — typically 2 to 6 weeks in mid to late summer (December-February in the Southern Hemisphere). Beekeepers truck their hives into manuka stands for the duration of the bloom and pull them out as soon as the manuka is finished, before the bees can backfill the same combs with nectar from other plants. The intensity of manuka flowering in any given year is weather-dependent and unpredictable, which is the primary supply constraint that keeps prices high.

The nectar itself is not what is bactericidal. The active antibacterial precursor in nectar is dihydroxyacetone (DHA), a simple three-carbon ketose. DHA concentration in fresh manuka nectar varies dramatically by individual plant genetics, year, and location — this is why two jars of honest, authentic Manuka can have vastly different MGO ratings.

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The DHA-to-MGO Conversion in the Honey Jar

The Adams 2009 paper (Carbohydrate Research) established the precise chemical pathway that distinguishes Manuka from all other honeys. The bees collect manuka nectar, transport it to the hive, and process it normally — reducing water content, adding enzymes, sealing the comb. Fresh-harvested Manuka honey contains high DHA but only modest MGO. Over the next 6 to 12 months in the jar at ambient temperature, DHA undergoes spontaneous non-enzymatic dehydration to methylglyoxal:

Dihydroxyacetone (DHA) → Methylglyoxal (MGO) + H₂O

This is a slow chemical process — not a fermentation, not enzymatic, simply a temperature-dependent dehydration reaction in a highly concentrated acidic sugar matrix. The conversion accelerates at warmer storage temperatures (37°C produces near-complete conversion in weeks; 4°C nearly halts it). Commercial Manuka producers typically warm-store fresh honey at controlled elevated temperatures (around 27-37°C) for several months to drive the conversion before bottling. The final MGO level is essentially fixed by the starting DHA concentration in the nectar — you cannot make a 100+ MGO honey into a 500+ by storing it longer.

This explains several otherwise puzzling features of the Manuka market:

• Two-tier label — many premium brands print both "MGO" and "DHA" content. The DHA number represents the residual conversion potential. A honey with high DHA and modest MGO will increase in MGO with time; a honey with all DHA already converted is at its peak.
• Honest "best-before" dates — unlike most foods where "use-by" is downside protection against spoilage, Manuka actually peaks in MGO mid-shelf-life.
• Fraud opportunity — an unscrupulous producer can spike DHA-poor honey with synthetic DHA and produce a high-MGO product that lacks the other authenticity markers of real Manuka. The MPI definition (below) was developed specifically to detect this.

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Mechanism: How MGO Kills Bacteria

Methylglyoxal is a reactive electrophile — one of the most reactive small molecules in human biology. It is also produced endogenously as a side-reaction of glycolysis (which is why every aerobic organism has a glyoxalase detoxification system to scavenge it). At the concentrations present in even modestly-rated Manuka (100+ mg/kg = 100+ ppm), MGO produces sustained, broad-spectrum bactericidal activity through several overlapping mechanisms:

• Protein alkylation — MGO reacts with arginine, lysine, and cysteine side chains, forming advanced glycation end-products (AGEs) on bacterial cell-surface and structural proteins. The protein modifications inactivate enzymes essential to bacterial replication and disrupt membrane proteins.
• DNA modification — MGO is one of the carbonyl compounds that react with DNA to form advanced glycation end-products such as N2-carboxyethyl-2'-deoxyguanosine (CEdG); in a laboratory study, genes carrying CEdG lost much of their function (Breyer 2008).
• Biofilm disruption — in laboratory studies, Manuka honey inhibited the development of Streptococcus pyogenes biofilms and permeated 24-hour established ones, killing cells (Maddocks 2012), and Manuka and Sidr honeys killed most bacteria in Staphylococcus aureus and Pseudomonas aeruginosa biofilms (Alandejani 2009). Maeda 2008 found that honey reduced counts of community-associated methicillin-resistant S. aureus (CA-MRSA) in culture. This matters because biofilms are a main reason chronic wounds resist standard antibiotic therapy.
• Synergy with the other three honey mechanisms — MGO works on top of the osmotic, peroxide, and acidic-pH effects of all honey. Manuka does not replace those mechanisms; it adds a fourth, potent direct-kill mechanism that ordinary honey lacks.

An important note on resistance: extensive in vitro work has failed to produce stable MGO-resistant mutants of clinically important bacteria. The proposed reason is that MGO acts through multiple non-specific protein and DNA targets simultaneously, leaving no single target for resistance mutations to address. This is in contrast to most antibiotics that target a single enzyme or pathway. The practical implication: Manuka and methicillin-resistant Staphylococcus aureus (MRSA), Manuka and Pseudomonas aeruginosa, Manuka and Enterococcus, Manuka and ESBL-producing E. coli all show consistent in-vitro and in-vivo kill curves even when the same organisms are resistant to most pharmacy antibiotics. See the Wound Healing page for the topical applications this enables.

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The Three Rating Systems (MGO, UMF, NPA)

Three rating systems coexist on the Manuka shelf. They measure essentially the same property in different ways:

• MGO (mg/kg) — the most direct measurement. Reports the actual measured methylglyoxal concentration in mg per kg of honey (equivalent to parts per million). Typical commercial range: MGO 30 (basic), MGO 100+ (entry premium), MGO 250+ (mid-premium), MGO 400+ (therapeutic-grade), MGO 550+ (high therapeutic), MGO 800+ and MGO 1,000+ (very-high-end therapeutic).
• UMF (Unique Manuka Factor) — the original rating system, developed by Peter Molan's lab at the University of Waikato in the 1990s. UMF compares the antibacterial activity of Manuka against a phenol standard in a zone-of-inhibition assay against Staphylococcus aureus. The UMF grade scale runs from UMF 5+ through UMF 10+, 15+ and 20+ to a top grade of UMF 25+. UMF licensing is administered by the Unique Manuka Factor Honey Association (UMFHA) in New Zealand. Modern UMF certification is a four-factor test of MGO, leptosperin, DHA and hydroxymethylfurfural (HMF, a freshness marker).
• NPA (Non-Peroxide Activity) — a generic descriptor for the antibacterial activity that remains after the hydrogen-peroxide-generating glucose oxidase is destroyed (typically by adding catalase or by heat-treating). NPA effectively isolates the MGO contribution. NPA values track UMF values closely (NPA 10 ≈ UMF 10).

The minimum MGO levels in the UMF Honey Association grading table:

• MGO 83 ≈ UMF 5+ ≈ NPA 5+
• MGO 261 ≈ UMF 10+ ≈ NPA 10+
• MGO 512 ≈ UMF 15+ ≈ NPA 15+
• MGO 826 ≈ UMF 20+ ≈ NPA 20+
• MGO 1,197 ≈ UMF 25+ ≈ NPA 25+

Some products use proprietary activity ratings that are not standardized scientific measurements and are not tied to measured methylglyoxal. If a jar does not show one of the three real ratings (MGO, UMF, or NPA), there is no way to compare its potency against anything else.

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The New Zealand MPI Scientific Definition

Authentic monofloral Manuka honey was for years defined only by pollen content (melissopalynology), which was easy to fake and easy to dispute. In 2018, the New Zealand Ministry for Primary Industries (MPI) introduced a science-based regulatory definition that all honey exported from New Zealand and labeled "Manuka" must meet. The MPI definition requires five tests:

1. 3-phenyllactic acid ≥ 400 mg/kg (monofloral) or ≥ 20 mg/kg (multifloral)
2. 2'-methoxyacetophenone ≥ 5 mg/kg
3. 2-methoxybenzoic acid ≥ 1 mg/kg
4. 4-hydroxyphenyllactic acid ≥ 1 mg/kg
5. DNA from Leptospermum scoparium — less than C_q 36 in a qPCR assay

All five tests must pass for "monofloral Manuka" certification. The thresholds were calibrated against known authentic Manuka samples and are difficult to fake by spiking with synthetic DHA, syrup adulteration, or pollen contamination. The MPI label on a jar (typically as an export certificate number or a "Made in New Zealand" mark backed by MPI testing) is the strongest single signal of authenticity available to consumers.

Australian Manuka honey (from Tasmanian and Victorian Leptospermum scoparium as well as several closely related Australian Leptospermum species) is not covered by the MPI definition. The Australian Manuka Honey Association (AMHA) maintains a parallel standard, but the New Zealand industry contests the use of the word "Manuka" by Australian producers in international markets. From a chemical and clinical-efficacy standpoint, both sources produce high-MGO honey.

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MGO Strengths Used for Different Applications

The general pattern: lower MGO grades are sold for oral use, higher MGO grades for topical wound use.

• Cough, sore throat, daily oral health — MGO 100+ to MGO 250+ (below UMF 10+ on the UMF table) is generally considered sufficient. Higher MGO adds little here because oral mucosa is well-perfused, the contact time is short, and the cost premium is large.
• Gastrointestinal use (e.g. occasional support for the gut) — MGO 250+ to MGO 400+ (between UMF 10+ and UMF 15+ on the UMF table). Higher grades add little because the honey is diluted in the gastrointestinal (GI) tract regardless.
• Topical use on minor wounds, abrasions, eczema — MGO 400+ and up. This is the level at which topical antibacterial activity is reliably superior to ordinary honey.
• Chronic wounds, burns, ulcers — clinical settings use U.S. Food and Drug Administration-cleared medical-grade manuka honey wound dressings rather than a food jar. Hospital-grade Manuka medical-device products are gamma-irradiated to eliminate Clostridium spores, packaged sterile, and standardized to high MGO concentrations equivalent to MGO 550+ to 800+.
• MGO 800+ and above — these are luxury-tier products. The clinical evidence for any incremental benefit over MGO 400+ in real use is thin. Most of the price difference reflects scarcity, not therapeutic advantage.

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Fraud and Watered-Down Manuka

The Manuka market has historically been plagued by fraud. Global sales of products labeled "Manuka" routinely exceed the entire New Zealand annual harvest by 3-to-1 or more — meaning the majority of jars on global shelves at any given time are partly or wholly counterfeit. Features that distinguish authentic product:

• Authentic Manuka comes from New Zealand or Australia, with the country of origin on the label
• Genuine potency labels give one of the three real ratings (MGO, UMF, or NPA) with a specific number
• UMF-graded products are tested batch by batch for MGO, leptosperin, DHA and HMF
• New Zealand export product carries an MPI export certificate or a statement that the honey meets the MPI five-test definition for monofloral Manuka
• "Manuka blend" or "Manuka with other floral sources" labels often contain very small fractions of real Manuka mixed with ordinary clover or rapeseed honey
• Unusually low prices are a warning sign — authentic UMF 15+ Manuka retails for approximately $40-60 USD per 250g jar in 2026
• Some proprietary "activity" numbers include the hydrogen-peroxide activity present in all honey, not just the non-peroxide Manuka activity, so they are not comparable with MGO, UMF or NPA values

For a deeper discussion of raw vs pasteurized labeling and other honey label terms, see the separate page in this Benefits hub.

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Australian vs New Zealand Manuka

Australian Leptospermum honey is chemically equivalent to New Zealand Manuka in terms of MGO content and antibacterial activity. The dispute is about the word "Manuka" itself, which has Maori linguistic and cultural roots in New Zealand and which the New Zealand industry has sought to protect as a geographical indication (analogous to "Champagne" or "Roquefort" in Europe).

From a clinical/therapeutic standpoint, an MGO-400 honey from Tasmania or Victoria is interchangeable with an MGO-400 honey from the Coromandel Peninsula. From a fraud-defense standpoint, the New Zealand product currently has the more developed regulatory framework (MPI five-test definition + UMF certification), and the Australian framework (AMHA) is newer. Honey labeled "Manuka" from countries with no Leptospermum trees cannot be genuine Manuka.

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Cautions

• Infant botulism — absolute contraindication under 12 months — this applies to Manuka exactly as it applies to all honey. Food-grade Manuka honey is not gamma-irradiated and can contain Clostridium botulinum spores. Honey, including Manuka, is not given to children under 12 months because these spores can cause infant botulism. The only exception is hospital medical-grade Manuka dressings, which are gamma-irradiated and labeled sterile — these are not for oral use.
• Diabetes management — Manuka honey is approximately 80% sugar (mostly fructose and glucose). The glycemic load is real. For oral use in cough or sore throat, the small spoonful dose adds little sugar; daily multi-tablespoon use adds a meaningful amount of carbohydrate. See the Diabetes page for context.
• Cost — high-MGO Manuka is one of the most expensive foods sold by weight. For applications where ordinary honey is sufficient (oral coughs, sweetener replacement), Manuka adds cost without an added benefit.
• Allergy — honey allergy is rare but can include anaphylaxis, especially in individuals sensitized to bee venom proteins or specific pollens. Manuka carries the same allergy risk as ordinary honey for people with a documented honey allergy.
• Dental caries — despite some marketing claims, Manuka honey is a fermentable sugar in the oral cavity and supports cariogenic bacterial growth on tooth surfaces. Honey left on the teeth, including honey on a child's pacifier at bedtime, feeds the bacteria that cause tooth decay.
• Drug interactions — Manuka has not been documented to interact with prescription medications at oral doses. Topical application to wounds in patients on systemic antibiotics is not contraindicated and may be synergistic.

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Key Research Papers

1. Mavric E, Wittmann S, Barth G, Henle T (2008). Identification and quantification of methylglyoxal as the dominant antibacterial constituent of Manuka (Leptospermum scoparium) honeys from New Zealand. Molecular Nutrition & Food Research. 52(4):483-9 — PubMed PMID: 18210383
2. Adams CJ, Manley-Harris M, Molan PC (2009). The origin of methylglyoxal in New Zealand manuka (Leptospermum scoparium) honey. Carbohydrate Research. 344(8):1050-3 — PubMed PMID: 19368902
3. Adams CJ et al. (2008). Isolation by HPLC and characterisation of the bioactive fraction of New Zealand manuka honey. Carbohydrate Research — PubMed PMID: 18194804
4. Allen KL, Molan PC, Reid GM (1991). A survey of the antibacterial activity of some New Zealand honeys. Journal of Pharmacy and Pharmacology. 43(12):817-22 — PubMed PMID: 1687577
5. Molan PC (1992). The antibacterial activity of honey: the nature of the antibacterial activity. Bee World. PubMed: Molan 1992
6. Atrott J, Henle T (2009). Methylglyoxal in Manuka honey — correlation with antibacterial properties. Czech Journal of Food Sciences. PubMed: Atrott-Henle 2009
7. Stephens JM et al. (2010). Phenolic compounds and methylglyoxal in some New Zealand manuka and kanuka honeys. Food Chemistry. PubMed: Stephens 2010
8. Maeda Y et al. (2008). Antibacterial activity of honey against community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA). Complementary Therapies in Clinical Practice. 14(2):77-82 — PubMed PMID: 18396250
9. Maddocks SE et al. (2012). Manuka honey inhibits the development of Streptococcus pyogenes biofilms and causes reduced expression of two fibronectin binding proteins. Microbiology. 158(Pt 3):781-790 — PubMed PMID: 22294681
10. Carter DA et al. (2016). Therapeutic Manuka Honey: No Longer So Alternative (review). Frontiers in Microbiology — PubMed PMID: 27148246
11. Roberts AEL, Maddocks SE, Cooper RA (2015). Manuka honey reduces the motility of Pseudomonas aeruginosa. PubMed PMID: 25404649
12. Alandejani T, Marsan J, Ferris W, Slinger R, Chan F (2009). Effectiveness of honey on Staphylococcus aureus and Pseudomonas aeruginosa biofilms. Otolaryngology–Head and Neck Surgery. 141(1):114-8 — PubMed PMID: 19559969
13. Breyer V, Frischmann M, Bidmon C, Schemm A, Schiebel K, Pischetsrieder M (2008). Analysis and biological relevance of advanced glycation end-products of DNA in eukaryotic cells. FEBS Journal. 275(5):914-25 — PubMed PMID: 18215162
14. Cokcetin NN et al. (2016). The antibacterial activity of Australian Leptospermum honey correlates with methylglyoxal levels. PLOS ONE — PubMed PMID: 28030589

PubMed Topic Searches

1. PubMed: MGO and Manuka antibacterial
2. PubMed: Manuka and MRSA wound
3. PubMed: Manuka and biofilms
4. PubMed: Leptospermum nectar DHA
5. PubMed: UMF rating

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Connections

• All Food
• Honey Main Page
• Honey Benefits Hub
• Raw vs Pasteurized
• Wound Healing Topical
• Cough Suppressant Evidence
• Wound Care
• Burns
• Methicillin-Resistant Staphylococcus Aureus
• Pseudomonas aeruginosa
• Diabetes (Foot Ulcer)
• Immune Boosting
• Remedies
• Tea Tree (Melaleuca)
• History
• Nutrients

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