What is E131?
Complete guide to understanding E131 (Patent Blue V) — a synthetic blue dye with limited food use
The Quick Answer
E131 (Patent Blue V) is a bright synthetic blue dye used to color specific foods in the EU and some other countries.
It’s more famous for its medical use — surgeons inject it into the body to identify lymph vessels and lymph nodes during cancer surgery.
It’s rare in mainstream food products because most major markets (US, Canada, Australia) banned it due to allergy concerns, and the EU restricts its use.
📌 Quick Facts
- Chemical Name: Patent Blue V or C.I. 42051
- Other Names: Food Blue 5, Sulphan Blue, Sky Blue, Acid Blue 3
- Category: Synthetic triphenylmethane dye (NOT an azo dye)
- Found in: Scotch eggs, jelly sweets, blue Curaçao, gelatin desserts, meat products (in EU only)
- Safety Status: Approved in EU; Banned in US, Canada, Australia, Norway
- Approved by: EFSA (EU only); not approved by FDA or equivalent in major markets
- Acceptable Daily Intake: 0-5 mg/kg body weight/day (EFSA 2013)
- Main Concern: Allergic reactions in susceptible individuals
What Exactly Is It?
E131 is a 100% synthetic blue dye created entirely in a laboratory from coal tar and petroleum-derived aromatic precursors.
Unlike E127 (erythrosine), E128 (Red 2G), and E129 (Allura Red), which are all azo dyes, E131 belongs to a different chemical class called triphenylmethane dyes.
A triphenylmethane dye consists of three benzene rings connected by a central carbon atom. This different structure means E131 is metabolized differently in your body than azo dyes — it doesn’t break down into aromatic amines like the red dyes do.
The chemical formula is C₅₄H₆₂CaN₄O₁₄S₄ when supplied as the calcium salt, or with sodium instead of calcium. In solution, it produces a vivid sky-blue color.
Where You’ll Find It
Food Products (EU — Very Limited Use)
E131 is NOT commonly found in mainstream foods, even in the EU where it’s approved. It appears in very specific product categories:
| Product Category | Examples | Rarity |
|---|---|---|
| Savoury Foods | Scotch eggs, minced meat, sausages, meat products, fish preparations | Uncommon |
| Confectionery | Jelly sweets, gummy candies, icings | Very rare |
| Desserts & Beverages | Gelatin desserts, puddings, blue Curaçao, alcoholic drinks | Very rare |
| Other | Fat-based desserts, cakes, biscuits, food supplements | Uncommon |
Even in these categories, E131 is used inconsistently. Most manufacturers prefer other approved blue dyes or avoid blue coloring altogether.
Medical & Non-Food Applications (MAJOR Use)
E131 is far more commonly used in medicine than in food:
– Lymphangiography: Surgeons inject Patent Blue V into the body to visualize lymph vessels during medical imaging
– Sentinel Node Biopsy: Critical use during cancer surgery — helps identify which lymph nodes to remove
– Dental Applications: Used in plaque disclosing tablets to show where plaque buildup occurs
– Research & Laboratory: Histological staining (Masson’s trichrome), pH indicator, analytical applications
This is why E131 is most commonly known to doctors and surgeons, not consumers.
Why Is It Banned in So Many Countries?
The Allergic Reaction Concern
The primary reason for bans: E131 can trigger allergic reactions in susceptible individuals.
Documented allergic reactions include:
– Mild to moderate: Itching, nettle rash (urticaria), nausea
– Systemic: Hypotension (low blood pressure)
– Rare but serious: Anaphylactic shock (life-threatening allergic reaction)
The allergic reactions are IgE-mediated (Type I hypersensitivity), meaning they occur quickly and are triggered by immune system recognition of the dye.
Risk Factors for Allergic Reactions
Reactions are most likely in:
– People with a history of food dye allergies or sensitivities
– Individuals with atopic conditions (asthma, eczema, hay fever)
– People allergic to other synthetic dyes
– Children (though reactions uncommon overall)
Not everyone will react — it’s individual susceptibility that determines risk.
Why This Led to Bans
Regulatory agencies in the US, Canada, Australia, and Norway concluded that the allergy risk outweighed the benefits of having a blue food dye.
Their risk-benefit analysis:
| Factor | Assessment |
|---|---|
| Benefit of blue coloring | Low-to-moderate; not essential; alternative colorants available |
| Risk of allergic reactions | Real and documented; potential for serious reactions |
| Vulnerable population | People with dye sensitivities; includes children |
| Decision | Ban E131; risk > benefit |
The EU made a different decision: Allow E131 but restrict use and exclude from infant/young children foods — balancing color choice for consumers against allergy risk.
Is It Safe?
The Official Position (EFSA)
The European Food Safety Authority (EFSA) says E131 is safe at approved use levels, but notes important caveats:
– ADI established: 0-5 mg/kg body weight/day (EFSA 2013)
– For 70 kg adult: ~350 mg per day allowed
– Typical consumption: Most EU consumers eat far below this limit
– Concern noted: At maximum permitted use levels, some high consumers (especially toddlers and children) may exceed the ADI
– Mitigation: Actual reported use levels are lower than permitted maximums; regulated to keep exposures below ADI for all populations
Toxicity Assessment
| Toxicology Parameter | Findings | Safety Implication |
|---|---|---|
| Chronic Toxicity (mice) | NOAEL 500 mg/kg body weight/day | High tolerance; no adverse effects at this level |
| Uncertainty Factor Applied | 100x (standard safety margin) | Very conservative safety approach |
| Resulting ADI | 5 mg/kg body weight/day | Considered safe |
| Genotoxicity | Standard battery of tests: Negative | No DNA damage concern |
| Carcinogenicity | Animal studies: Negative | No cancer risk documented |
The Allergy Issue (Not Captured in Toxicity Assessments)
Important distinction: Allergic reactions are NOT considered in traditional toxicity/ADI assessments.
The EFSA’s toxicity evaluation (what led to ADI of 5 mg/kg) is based on:
– Effects on organ systems (liver, kidney, etc.)
– Potential for DNA damage
– Potential for cancer
– Acute toxicity
But allergic reactions are immune-mediated individual responses, not “toxic” effects in the traditional sense. They affect only susceptible people, not everyone.
This is why:
– EFSA said: “E131 is toxicologically safe” → Approved with restrictions
– FDA/Health Canada/FSANZ said: “Allergy risk is unacceptable” → Banned
Both conclusions can be scientifically justified; they reflect different regulatory philosophies toward allergy risk.
Natural vs. Synthetic
E131 is 100% synthetic. There is no natural version of Patent Blue V found in nature.
All commercial E131 is manufactured through industrial chemistry from petroleum-derived aromatic compounds.
Natural Alternatives to E131
Limited natural blue colorants exist:
| Alternative | Source | Status | Challenges |
|---|---|---|---|
| Blue Spirulina (Phycocyanin) | Algae (Spirulina platensis) | Natural, increasingly available | Expensive; limited availability; mild blue shade |
| Butterfly Pea Flower | Plant extract (Clitoria ternatea) | Natural, traditional use in Southeast Asia | Very expensive; pH-sensitive color changes |
| E133 (Brilliant Blue FCF) | Synthetic (FDA/EU approved) | Synthetic but more widely approved than E131 | Not truly “natural” but available in more markets |
The lack of affordable, stable natural blue dyes is why manufacturers still use synthetic blues — but they typically prefer E133 (Brilliant Blue FCF) over E131 because E133 is approved in more countries and has lower documented allergy risk.
Why E131 Is Rarely Discussed
E131 is one of the least well-known synthetic food dyes because:
1. Already banned in major markets: US, Canada, Australia, Norway represent ~40% of global food market; many manufacturers don’t even consider it
2. Limited EU use: Even in the EU where approved, it’s uncommon in mass-market products
3. Medical applications dominate: Most E131 production goes to medical/pharmaceutical use (surgery), not food
4. Reputation: Association with allergic reactions discourages use
5. Better alternatives available: Other blue dyes (E133) approved in more countries
6. Less controversial: No major scandal or recent ban like E127 (US 2025) or E128 (EU 2007) keeps it in headlines
Ongoing Regulatory Scrutiny
The Bottom Line
E131 (Patent Blue V) is a synthetic blue dye approved in the EU but banned in most other major markets due to allergy risk.
What you should know:
- It’s rare in food: Most foods don’t contain it; very limited use even in the EU
- Its real use is medical: Surgeons inject it during cancer operations to find lymph nodes
- It can trigger allergies: In susceptible individuals, causing itching, rash, nausea, or rarely, anaphylaxis
- It’s toxicologically safe: At permitted levels, traditional toxicity testing shows no concerns
- Allergy risk caused bans: US, Canada, Australia, Norway decided allergy risk > benefits; EU disagreed
- High consumers may exceed ADI: EFSA noted some children at maximum permitted use levels might exceed safe intake
- It’s getting renewed scrutiny: EFSA’s 2025 call for data suggests ongoing regulatory evaluation