Common Name(s): Ci 15510,orange ii,para-naphtholazobenzene

CAS Number: 633-96-5

DESCRIPTION

What It Does: Provides orange acid-condition hair tinting.

Why It's Used: Classic acid orange hair dye for salon acidic tinting formulations providing warm orange tones.

How It Works: Anionic sulfonate groups provide water solubility. at acidic ph (below hair keratin isoelectric point ~3.7) the hair surface acquires positive charge, enabling ionic interaction with anionic acid dye. rinse at higher ph causes dye release (semi-permanent character).

Typically Found In: Acid hair tints,semi-permanent orange toners

TECHNICAL DETAILS

Primary Category: Hair colourant – acid dye

Secondary Functions: Skin conditioning

Application Areas:

Typical Concentration Range: 0.01%–2%

SOURCING & ETHICS

Vegan Status: Yes – synthetic

Halal Status: Yes

Source Notes: Commercially produced for cosmetic use. verify vegan/halal status with supplier.

SKIN COMPATIBILITY

Irritancy Rating: 1/5 – very low

Comedogenicity Rating: 0/5 – non-comedogenic

Sensitivity Concerns: Well-tolerated by most skin types.

Safe for Sensitive Skin: Yes

SAFETY & COMPATIBILITY

Safety Profile: Eu annex iv colorant list; not approved as hair dye in some jurisdictions. verify regulatory status for hair dye application.

Works Well With: Standard skincare actives

Avoid Combining With: No known significant incompatibilities

SCIENTIFIC NOTE

Acid dye substantivity to hair at low ph (below the isoelectric point ~3.7) provides a unique ph-responsive colouring mechanism: at ph <3.7, hair proteins acquire a net positive charge (from protonated amino groups exceeding ionized carboxyl groups), enabling ionic binding of anionic acid dye anions. this ph-gated substantivity means acid dyes wash out gradually as the hair environment returns to normal ph 4.5-5.5 during styling.

Last Verified: Cosing database,eu annex iv

Primary Sources: 2026-03-12