# methylene blue

CEFR C2 · Compound

Source: https://englishreference.com/word/methylene-blue
Updated: 2026-10-15

## Definition

a dark green powder that turns deep blue when you mix it with water. It is used as a dye, a medicine for certain blood problems, and in science labs to stain cells so they are easier to see.

For teachers: a heterocyclic aromatic chemical compound used as a biological stain, a chemical indicator, and a medication for treating methemoglobinemia. It appears as a dark green crystalline powder at room temperature but produces a deep blue solution in water.

## Examples

- The scientist used methylene blue to see the cells under the microscope.
- Doctors administered methylene blue to the patient to treat a rare condition that prevented their blood from carrying oxygen properly.
- In microbiology, methylene blue serves as a vital stain, allowing researchers to differentiate between living and dead cells based on their ability to reduce the dye to a colorless form.

## Usage notes

- Often used with 'stain' or 'dye' in laboratory contexts.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.