Ingredient review
Hydroxyethyl-2-Nitro-P-Toluidine
INCI: HYDROXYETHYL-2-NITRO-P-TOLUIDINE
A synthetic yellow dye used in hair color; generally considered safe in small amounts but may cause irritation for sensitive scalps.
In plain English
This is a man-made yellow dye that helps give hair color its shade. It's mostly found in semi-permanent and permanent hair dyes. While it's approved for use in many countries, it can sometimes cause mild irritation if you have a sensitive scalp or allergies to hair dye ingredients.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Main practical flags: irritation is moderate; clogging risk is low.
- Source
- synthetic
- Evidence
- moderate
- Irritation
- moderate
- Clogging risk
- low
Quick decision guide
Useful, but context matters
Hydroxyethyl-2-Nitro-P-Toluidine can be useful, but watch for some irritation potential.
Plain-English read
Treat this as a practical screening step before you compare products that contain this ingredient.
- Step 1Start with the score, then check the irritation and clogging risk before judging Hydroxyethyl-2-Nitro-P-Toluidine.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.
Score terms in plain English
Irritation risk
moderateCan bother some users, especially with frequent use, damaged skin, or strong companion ingredients.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
A synthetic nitro dye that imparts a yellow hue to hair. It belongs to a class of colorants known as nitro dyes, which are commonly used in oxidative and direct hair dyes.
How it works
It deposits color onto the hair shaft by binding to the hair's outer layer (cuticle). In oxidative dyes, it reacts with other dye precursors and hydrogen peroxide to form larger color molecules that become trapped inside the hair.
Pros
Effective yellow colorant
Provides consistent and bright yellow tones that are stable in hair dye formulations.
Widely used and regulated
Approved for use in hair dyes by many global regulatory bodies, including the EU and FDA, at specified concentrations.
Cons and cautions
Potential irritant
Can cause mild to moderate skin irritation, especially for those with sensitive scalps or pre-existing skin conditions.
Allergen risk
Like many synthetic hair dye ingredients, it may trigger allergic reactions in susceptible individuals, particularly with repeated use.
Best for
- People looking for yellow tones in semi-permanent or permanent hair color
- Those without known sensitivities to hair dye ingredients
Use caution if
- Individuals with known allergies to PPD (paraphenylenediamine) or other hair dye ingredients
- People with very sensitive or damaged scalps
Usage tips
Safety summary
Generally recognized as safe for use in hair dyes at low concentrations, but may cause skin irritation or allergic reactions in sensitive individuals. Patch testing is strongly advised.
Research notes
Studies indicate low acute toxicity and no significant carcinogenic risk at typical use levels. However, some individuals may experience contact dermatitis. More research is needed on long-term cumulative exposure.
Common label clues
- Typical concentration
- Up to 1.5% in rinse-off hair products
- Regulatory status
- Approved for use in hair dyes in the EU (CosIng database) and by the US FDA as a color additive for hair dyes, subject to concentration limits.
- Common uses
- Hair dyes, Temporary and semi-permanent hair color
- Environmental note
- Synthetic dyes can persist in wastewater; proper disposal of hair dye products is recommended to minimize environmental impact.
Good to know
- This ingredient is often listed under the name HC Yellow No. 2 on product labels.
- It is typically used in combination with other dyes to achieve a range of shades.
Common questions
What is Hydroxyethyl-2-Nitro-P-Toluidine in beauty products?
This is a man-made yellow dye that helps give hair color its shade. It's mostly found in semi-permanent and permanent hair dyes. While it's approved for use in many countries, it can sometimes cause mild irritation if you have a sensitive scalp or allergies to hair dye ingredients.
What does Hydroxyethyl-2-Nitro-P-Toluidine do in a beauty product?
It deposits color onto the hair shaft by binding to the hair's outer layer (cuticle). In oxidative dyes, it reacts with other dye precursors and hydrogen peroxide to form larger color molecules that become trapped inside the hair.
Is Hydroxyethyl-2-Nitro-P-Toluidine safe for most people?
Generally recognized as safe for use in hair dyes at low concentrations, but may cause skin irritation or allergic reactions in sensitive individuals. Patch testing is strongly advised.
Who should be careful with Hydroxyethyl-2-Nitro-P-Toluidine?
Individuals with known allergies to PPD (paraphenylenediamine) or other hair dye ingredients People with very sensitive or damaged scalps
Research sources
Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.