Methylene Blue
- Dyes & colorants
- CAS 61-73-4
- IUPAC: 3,7-bis(Dimethylamino)phenothiazin-5-ium chloride
CarCareTruth tracks Methylene Blue (CAS 61-73-4) as a car-care ingredient.
At 0.1–1% concentration in consumer formulas, the product-level mixture is Not classified under GHS-US. At ingredient level: H302 (Harmful if swallowed, oral toxicity Cat 4, LD50 oral rat 1,180 mg/kg), H318 (Causes serious eye damage, Eye Dam. 1). The intense blue dye stains skin and fabric on contact. In laboratory/medical contexts, higher concentrations carry additional hazards.
Methylene Blue is a synthetic phenothiazine dye and the most common colorant in windshield washer fluids, giving products their characteristic vivid blue appearance. At the concentrations used in consumer cleaning products (typically 0.1–1%), the mixture-level GHS classification is Not classified, though the ingredient itself carries H302 (oral toxicity Cat 4) and H318 (serious eye damage) at ingredient level.
The dye is notable for its intense staining properties: it readily causes persistent skin staining that can last several days. This cosmetic hazard is not captured in the GHS classification but is a real consumer concern.
From an environmental standpoint, methylene blue is aquatic-toxic (H402/H412) and resistant to conventional biodegradation, which is why products using it at higher concentrations can receive environment deductions despite the low health profile at use concentrations.
Health & environment profile
- VOC
- no
- Prop 65 listed
- no
- Asthmagen
- no
- EPA Safer Choice
- no
- Aquatic toxicity
- yes
- Biodegradable
- no
- Bioaccumulative
- no
- Persistent
- no
- Ozone depleting
- no
- Microplastic
- no
- PFAS
- no
- Env. score
- 2/5
Common questions about Methylene Blue
- What is Methylene Blue used for in car care?
- Blue dye used to color windshield washer fluid and other cleaning products for identification and visual appeal
- Is Methylene Blue a VOC?
- No. Methylene Blue is not classified as a volatile organic compound (VOC).
- Is Methylene Blue on California's Proposition 65 list?
- No. Methylene Blue is not on California's Proposition 65 list.
No products on file contain this (yet)
Related
Health and environment notes translate the manufacturer Safety Data Sheet, the GHS classification, and authoritative regulatory listings (California Prop 65, EPA). Not medical advice. They describe the ingredient itself; whether a hazard applies to a finished product depends on its concentration and how it's used.