chemistry

Erythrosine

Erythrosine is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Erythrosine rather than just read about it. In short: Erythrosine, also known as E127 and Red No. 3, is an organoiodine compound, specifically a derivative of fluorone. It is a red-pink dye used for food coloring, cosmetics, hair coloring, pet products, and diverse industrial colorings.

Key takeaways

Erythrosine belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Erythrosine to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Erythrosine from memory before moving on to harder problems.

Reference excerpt

Erythrosine, also known as E127 and Red No. 3, is an organoiodine compound, specifically a derivative of fluorone. It is a red-pink dye used for food coloring, cosmetics, hair coloring, pet products, and diverse industrial colorings. It is the disodium salt of 2,4,5,7-tetraiodofluorescein.

History

The colorant was discovered by the Swiss chemist Karl Kussmaul at the University of Basel in 1876 and soon commercialized by the local Bindschedler & Busch company for dyeing wool and silk. Its use as a textile dye was soon superseded due to its propensity to fade in sunlight. Its use as a food dye was legalized in the US by the Pure Food and Drug Act of 1906. By early 1920s, it was produced mainly for the food industry, with 2,170 pounds (0.98 t) made in America in 1924, rising to 9,468 pounds (4.29 t) in 1938 and approximately 50 tons in 1967.

Production Erythrosine is synthesized from resorcinol and phthalic anhydride, which are processed into fluorescein. Fluorescein then undergoes iodination, producing the bright red dye.

Uses It is used as a food coloring, printing ink, biological stain, dental plaque disclosing agent, radiopaque medium, sensitizer for orthochromatic photographic films, and visible light photoredox catalyst. Erythrosine is commonly used in sweets, such as some candies, ice pops and cherries, and in cake-decorating gels. It was also used to color pistachio shells. As a food additive, it has the E number E127.

Safety assessment and regulation Laboratory studies in the late 20th century suggested that "chronic erythrosine ingestion may promote thyroid tumor formation in rats via chronic stimulation of the thyroid by TSH" at concentrations of 4% erythrosine. Toxicology tests combined with a review of other reported studies concluded that erythrosine is non-genotoxic and any tumor growth results from a non-genotoxic mechanism. In the United States, laboratory evidence of carcinogenicity of extremely high doses of erythrosine renders it as "unsafe" under federal law by a provision called the Delaney Clause, despite conclusions by the federal Center for Food Safety and Applied Nutrition and Cancer Assessment Committee that the risk of developing cancer in humans is unlikely at the low erythrosine levels consumed as a food color. Throughout the early 21st century, the World Health Organization and several national food safety agencies permitted use of erythrosine as a color additive when used in amounts below acceptable daily intake levels for certain foods, such as for packaged cherries; countries having restricted-use provisions were the European Union, United States, Canada, and Australia/New Zealand. Since 1994, the European Food Safety Authority has only allowed erythrosine in processed cherries, pet foods, and up to 25 ppm in toothpaste. In the United Kingdom, it is also allowed for coloring eggshells. It may not be sold directly to consumers. In the United States, the use of erythrosine in cosmetics, topical drugs, some foods, and in all uses as its lake variant have been banned by the Food and Drug Administration (FDA) since 1990. In January 2025, the FDA banned the use of erythrosine in all foods and ingested drugs, with enforcement beginning on 15 January 2027 and 18 January 2028, respectively. An October 2023 bill passed in the state of California also banned the use of erythrosine in foods (along with brominated vegetable oil, potassium bromate, and propylparaben), with enforcement beginning on 1 January 2027. In 2025, Health Canada stated that erythrosine "does not pose a health risk to the general Canadian population at the levels set out in the List of Permitted Food Colours."

Synonyms Erythrosine B; Erythrosin B; Acid Red 51; C.I. 45430; FD&C Red No. 3; E127; 2',4',5',7'-Tetraiodo-3',6'-dihydroxy-spiro[3H-isobenzofuran-1,9'-xanthen]-3-one disodium salt; Tetraiodofluorescein sodium salt; Calcoid Erythrosine N; 2,4,5,7-Tetraiodo-3,6-dihydroxyxanthene-9-spiro-1'-3H-isobenzofuran-3'-one disodium salt; 2',4',5',7'-Tetraiodofluorescein, disodium salt; C.I. Food Red 14; Aizen Erythrosine; Tetraiodifluorescein, disodium salt; Spiro[isobenzofuran- 1(3H),9'-[9H]xanthen]-3-one, 3',6'-dihydroxy-2',4',5',7'-tetraiodo-, disodium salt.

Classification It is listed under the following number systems:

FD&C Red No. 3 E number E127 (Food Red 14) Colour Index no. 45430 (Acid Red 51) Bureau of Indian Standards No. 1697

References

Illustrations

Worked examples

Example 1 — a first encounter with Erythrosine

Start with the simplest possible case. Write down what Erythrosine claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Erythrosine before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Erythrosine ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Erythrosine

In research: Erythrosine appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Erythrosine in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Erythrosine is common in secondary-school and first-year university syllabi. It links to neighbouring topics 9-phenylfluorone dyes, E-number additives, Food colorings, so understanding it makes those chapters shorter.
In everyday life: Look for Erythrosine outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Erythrosine in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Erythrosine means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Erythrosine out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Erythrosine in simple terms?

Why does Erythrosine matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Erythrosine?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Erythrosine.