Common Name(s): 2-hydroxy-1,4-naphthoquinone,henna active
CAS Number: 83-72-7
DESCRIPTION
What It Does: Provides permanent natural hair colour through covalent keratin-reactive michael addition chemistry.
Why It's Used: The only natural permanent hair dye – lawsone's covalent bonding to keratin provides permanence that semi-permanent direct dyes cannot achieve.
How It Works: Hydroxyl group adjacent to quinone carbonyl provides highly reactive michael acceptor. cysteine thiols (–sh) in keratin perform michael addition to lawsone's 3-position, forming a covalent colour. permanent – only removed by bleach (destroys chromophore) or regrowth.
Typically Found In: Natural hair colouring (henna products)
TECHNICAL DETAILS
Primary Category: Hair colourant – natural keratin-reactive
Secondary Functions: Skin conditioning
Application Areas:
Facial Skincare
Body Care
Hair Care
Beard Care
Color Cosmetics (Makeup)
Dietary/Oral Supplements
Typical Concentration Range: 0.1%–pure (as henna powder)
SOURCING & ETHICS
Vegan Status: Conditional - supplier confirmation required
Halal Status: Unverified - supplier confirmation required
Source Notes: Black henna contains ppd added to henna – this is not natural henna and causes severe ppd sensitisation. pure henna without ppd is orange-red only. [audit 2026-07-29 rev2: the record's own source_notes does not assert a non-animal origin, or instructs the reader to verify with the supplier; "yes" asserts knowledge the record does not hold. determination requires shariah-panel sign-off.]
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: Good safety profile at recommended concentrations. ewg score: 1–2.
Works Well With: Standard skincare actives
Avoid Combining With: No known significant incompatibilities
SCIENTIFIC NOTE
Lawsone's michael addition to keratin creates a remarkable in-vivo dye chemistry: the reaction occurs at ambient temperature (no heating), at mild alkaline ph (achievable with slightly alkaline water), and produces a stable covalent bond that survives shampooing, uv exposure, and heat styling. this reaction selectivity and mild conditions under which covalent bond formation occurs is unique among cosmetic colourants.
Last Verified: 2026-03-12
Primary Sources: Cosing database,cir safety assessment,henna chemistry review