On this page
Key takeaways
• Fisetin is a flavonol — a subclass of the flavonoid polyphenols — with the chemical formula C₁₅H₁₀O₆ and IUPAC name 3,3′,4′,7-tetrahydroxyflavone (1).
• Dietary sources: strawberries are the richest food source at approximately 160 μg per gram fresh weight; apples, persimmons, grapes, onions, and cucumbers contain smaller amounts (2).
• Average dietary intake in typical Western diets is estimated at 0.4 to 1 mg per day — several hundredfold below any studied supplement dose (2).
• Supplement extraction is typically from the smoke tree (Rhus cotinus / Cotinus coggygria) or fustic wood, standardised to 98–99% purity (4).
• The senolytic identity was established by the 2018 Yousefzadeh paper, which identified fisetin as the most potent of ten tested flavonoids at selectively killing senescent cells (3).
Quick answer
Fisetin is a naturally occurring plant compound — chemically a flavonol — best known as the yellow-orange pigment in strawberries and other fruits. In supplement form, it is being investigated for its ability to selectively kill senescent cells (cells that no longer divide but continue to secrete inflammatory factors), a property called senolytic activity (3). This is a legitimate research direction with strong preclinical support and unresolved human clinical evidence. For the full evidence review across benefits, dose, and safety, see our complete clinician’s guide to fisetin.
The chemistry — what fisetin actually is
Fisetin (systematic name 3,3′,4′,7-tetrahydroxyflavone) belongs to the flavonol subclass of flavonoids. Flavonoids are a large family of plant-produced polyphenolic compounds characterised by a fused three-ring core structure — two benzene rings connected by a heterocyclic pyranone ring. Flavonols specifically carry a hydroxyl group at the C3 position on that middle ring, which distinguishes them from other flavonoid subclasses like flavones (apigenin, luteolin) and flavanones.
What distinguishes fisetin from its closest chemical relatives is the specific pattern of hydroxyl groups — four in total, positioned at the 3, 3′, 4′, and 7 positions on the flavonol backbone (4). Quercetin, its most similar structural sibling, carries an additional hydroxyl at position 5. That one-atom difference has meaningful biological consequences: it changes protein binding, antioxidant activity, and, critically for the longevity story, senolytic potency in cell culture (3). The compound was first isolated and characterised by the Austrian chemist Josef Herzig in 1891 from the smoke tree (Cotinus coggygria), historically used as a natural yellow dye (8). Its name derives from Rhus fustet, an old name for the smoke tree.
Where fisetin comes from — dietary sources
Fisetin is present in a wide range of fruits and vegetables but at meaningful concentrations in only a small subset. The Kimira 2019 analysis catalogued fisetin content across the standard Japanese diet and established the ranked list most commonly cited (2).
|
Food source |
Fisetin (μg per g fresh weight) |
Practical meaning |
|
Strawberries |
~160 |
The richest dietary source by a wide margin |
|
Apples (with skin) |
~27 |
A large apple provides several hundred μg |
|
Persimmons |
~11 |
Meaningful in cultures where persimmons are eaten daily |
|
Onions |
~5 |
Small per-serving contribution |
|
Grapes |
~4 |
Small contribution; higher in skin than flesh |
|
Cucumbers |
~1 |
Trace amount |
A 250 g serving of strawberries — roughly one small punnet — delivers approximately 40 mg of fisetin. This is well above the estimated average dietary daily intake of 0.4 to 1 mg (2) but still far below the doses used in supplement capsules (typically 100 to 500 mg) or in mouse senolytic studies (equivalent to thousands of milligrams per human 70 kg body weight). Diet cannot substitute for supplement dosing at senolytic levels — but sustained dietary polyphenol intake has its own independent evidence base for cardiovascular and cognitive outcomes. Our dedicated foods high in fisetin article ranks the sources with practical meal-planning guidance.
Where supplement fisetin comes from
Commercial fisetin supplements are almost never derived from strawberries, apples, or other food sources — extraction efficiency and cost make this impractical. The two principal sources are:
Smoke tree (*Rhus cotinus* / *Cotinus coggygria*)
Smoke tree leaves and heartwood contain fisetin at concentrations 100 to 1,000 times higher than any dietary source — approximately 30 to 50 mg per gram in dried leaves. This is the primary commercial source for high-purity extract, and the reason many labels list Rhus succedanea or Cotinus coggygria as the botanical source (4). The plant has a long history in traditional herbal medicine and as a natural yellow dye. When a fisetin capsule advertises 98% or 99% purity, this is the raw material behind it.
Fustic wood extract
Fustic wood, a related dye source, is an alternative botanical origin for commercial fisetin. Extraction, purification, and standardisation are largely equivalent to the smoke tree extract process. There is no clear evidence that fisetin from one source is biologically different from fisetin from the other — the molecule is the molecule.
A word on supply-chain purity
Not all commercial fisetin is equal. Independent testing has repeatedly found that fisetin powders sold on major consumer platforms can contain substantially less fisetin than the label states — in some reports, less than 50% of labelled amount, with rare cases below 1%. The load-bearing quality signal is a batch-specific third-party Certificate of Analysis from an ISO 17025-accredited laboratory. Our best fisetin supplement article walks through the criteria a careful buyer should apply.
How fisetin works in the body — the short version
Fisetin has three overlapping identities in the biological literature, which is one reason the marketing landscape can be confusing. Each identity is genuinely supported, though at different evidence tiers.
Antioxidant flavonoid
The oldest and most established identity. Fisetin scavenges reactive oxygen species directly, via its four hydroxyl groups, and indirectly through activation of the Nrf2 antioxidant response pathway, which upregulates glutathione synthesis and endogenous antioxidant enzymes (6). This is standard flavonoid pharmacology and applies to a large class of dietary polyphenols.
Anti-inflammatory compound
Fisetin suppresses NF-κB signalling in cell and animal models, reducing the transcription of pro-inflammatory cytokines (IL-6, TNF-α, IL-1β) across multiple tissue contexts (5,6). This anti-inflammatory identity underlies claims about fisetin for allergies, asthma, joint pain, and mast cell disorders.
Senolytic
The identity that made fisetin famous. In 2018, Yousefzadeh and colleagues at the Mayo Clinic screened ten flavonoid polyphenols against senescent cells and identified fisetin as the most potent at inducing selective apoptosis — killing senescent cells while sparing healthy dividing cells (3). In vivo, intermittent oral dosing in mice reduced senescent-cell markers across multiple tissues and extended median lifespan. This is the identity that drives the current commercial and research interest. For the full mechanistic biology and the ongoing human trials, see our dedicated senolytic article.
The bioavailability caveat — why the dose in the capsule isn’t the dose in the blood
Fisetin is poorly water-soluble and rapidly metabolised after oral absorption. The first — and, to date, only — published human pharmacokinetic study of unformulated oral fisetin (Krishnakumar 2022) gave 15 healthy adults 1,000 mg and measured plasma levels over 12 hours (7). The peak concentration of the parent compound was 9.97 ng/ml, roughly 35 nanomolar — very low relative to the concentrations at which fisetin clears senescent cells in cell culture (1–5 μM). Fisetin was undetectable in plasma beyond two hours.
This bioavailability ceiling is the practical caveat that shapes how much of fisetin’s cell-culture and mouse pharmacology can be expected to translate to a swallowed capsule in a human adult. Formulation strategies (liposomal, hydrogel-encapsulated, nano-particle) exist to close some of that gap, and the Krishnakumar hydrogel data showed a 23-fold improvement — but most commercial capsules are unformulated. Our dedicated bioavailability article walks through the pharmacokinetics, and our liposomal fisetin article evaluates the formulation options.
What we still don't know
• Whether the plant matrix matters. Dietary fisetin from strawberries is consumed in the context of vitamin C, anthocyanins, ellagic acid, and other polyphenols. Whether isolated capsule fisetin produces the same effects as fisetin-in-strawberries at equivalent doses is untested.
• The exact role of the geraldol metabolite. Fisetin is rapidly methylated to geraldol after absorption, and plasma concentrations of geraldol exceed those of the parent compound within the first hour (7). Some of fisetin’s biological activity may belong to the metabolite. This is not fully characterised.
• Long-term dietary intake and health outcomes. Epidemiological studies of flavonol intake and mortality exist, but fisetin-specific dietary intake versus outcome studies are limited.
Bottom line
Fisetin is a flavonol — a specific chemical class of plant compound — most abundant in strawberries and being investigated as a senolytic (a class of drugs that selectively clear senescent cells). The dietary intake floor is small; the supplement intake ceiling is limited by poor oral bioavailability. The chemistry is well characterised, the botanical origin is straightforward, and the biological effects are real but concentrated in cell culture and mouse studies. What fisetin does in a human adult taking a daily capsule is the question the ongoing clinical trials are designed to answer. For the complete clinical picture, see our full pillar guide.
Frequently asked questions
Is fisetin a drug?
No. Fisetin is classified as a dietary supplement and a naturally occurring plant compound. It is not licensed as a pharmaceutical in any major regulatory jurisdiction. It has been designated GRAS (Generally Recognized As Safe) in some formulations used in food applications.
Is fisetin a peptide?
No. Fisetin is a small-molecule flavonoid (molecular weight 286 daltons), not a peptide. Peptides are short chains of amino acids; fisetin is a polyphenol built on a flavonol backbone.
Is fisetin the same as quercetin?
No, but they are close chemical relatives. Both are flavonols. Quercetin has an additional hydroxyl group at position 5 that fisetin lacks. In cell culture, fisetin is a more potent senolytic than quercetin. In humans, quercetin has more clinical trial data overall. Our fisetin vs quercetin article covers the differences in depth.
How do you pronounce fisetin?
"FYE-suh-tin" is the most common English pronunciation, with the stress on the first syllable. The name derives from the Old French fustet (smoke tree).
Is fisetin fat-soluble or water-soluble?
Fisetin is fat-soluble (lipophilic). It is poorly soluble in water, which contributes directly to its low oral bioavailability. Taking fisetin with a fat-containing meal is one practical intervention for improving absorption (7).
Where can I read more about the senolytic biology?
Our dedicated senolytic article walks through the founding Yousefzadeh 2018 paper, the current human trial pipeline, and the honest question of whether the biology translates from mouse to human at supplement doses.
References
1. Fisetin — chemical entry. PubChem CID 5281614, National Center for Biotechnology Information. https://pubchem.ncbi.nlm.nih.gov/compound/5281614
2. Kimira Y, Osada A, Kimura M, et al. Contents of a bioactive flavonoid fisetin in fruits and vegetables used in the average Japanese diet. J Nutr Sci Vitaminol. 2019;65(5):443-447. https://pubmed.ncbi.nlm.nih.gov/31666481/
3. Yousefzadeh MJ, Zhu Y, McGowan SJ, et al. Fisetin is a senotherapeutic that extends health and lifespan. EBioMedicine. 2018;36:18-28. https://pmc.ncbi.nlm.nih.gov/articles/PMC6197652/
4. Grynkiewicz G, Demchuk OM. New perspectives for fisetin. Front Chem. 2019;7:697. https://pmc.ncbi.nlm.nih.gov/articles/PMC6817492/
5. Elsallabi O, Patruno A, Pesce M, et al. Fisetin as a senotherapeutic agent: biopharmaceutical properties and crosstalk between cell senescence and neuroprotection. Molecules. 2022;27(3):738. https://pmc.ncbi.nlm.nih.gov/articles/PMC8838024/
6. Khan N, Syed DN, Ahmad N, Mukhtar H. Fisetin: a dietary antioxidant for health promotion. Antioxid Redox Signal. 2013;19(2):151-162. https://pmc.ncbi.nlm.nih.gov/articles/PMC3689181/
7. Krishnakumar IM, Jaja-Chimedza A, Joseph A, et al. Enhanced bioavailability and pharmacokinetics of a novel hybrid-hydrogel formulation of fisetin orally administered in healthy individuals. J Nutr Sci. 2022;11:e74. https://doi.org/10.1017/jns.2022.72
8. Herzig J. Studien über natürlich vorkommende Flavone. VI. Über Fisetin. Monatshefte für Chemie. 1891;12(1):161-176. https://link.springer.com/article/10.1007/BF01517954