Lawsone is the principal coloring molecule found in the leaves of henna, primarily Lawsonia inermis L., a flowering shrub belonging to the Lythraceae family. The plant has historically also been referred to as Lawsonia alba and Lawsonia spinosa.

The leaves are dried and commonly powdered to produce henna preparations. Lawsone, chemically known as 2-hydroxy-1,4-naphthoquinone, is responsible for the characteristic orange-red to reddish-brown coloration produced by henna.

Chemical Information

Lawsone is a naturally occurring naphthoquinone derivative. Its chemical structure contains a hydroxyl group and a quinone system, which are important for its characteristic color and its ability to interact with proteins.

INCI Name: Lawsonia Inermis Leaf Extract
Chemical Name: 2-Hydroxy-1,4-naphthoquinone
CAS Number: 83-72-7
Chemical Class: Naphthoquinone
Molecular Formula: C10H6O3
Molecular Weight: 174.15 g/mol

The exact INCI designation depends on whether the cosmetic raw material is the whole plant material, a leaf extract or isolated lawsone. The specification supplied by the raw material manufacturer should therefore always be checked.

Function

Lawsone functions primarily as a natural colorant and hair-coloring agent. It is particularly notable for its ability to interact with keratin, allowing the pigment to become substantively associated with hair and skin.

Experimental research has also investigated antimicrobial and antioxidant properties associated with lawsone and henna extracts.

Hair Coloring

Henna has been used as a natural hair colorant for thousands of years. The coloring effect is primarily attributed to lawsone present in the leaves of Lawsonia inermis.

Unlike some synthetic or metallic hair dyes, lawsone does not simply form a superficial colored coating over the hair. The molecule has an affinity for keratin and can bind to keratin proteins, producing a durable orange-red to auburn coloration.

The final color depends on the natural hair color, hair structure, amount and quality of lawsone, application conditions, processing time and whether henna is combined with other botanical colorants.

Henna can also be used as a hair-conditioning and color-enhancing treatment, particularly where warm chestnut, copper or auburn tones are desired.

Interaction with Keratin

One of the most important characteristics of lawsone is its substantivity toward keratin.

Lawsone can react with amino groups present in keratin proteins, forming covalent or strongly associated colored products. This interaction allows the pigment to become incorporated into the outer structure of the hair rather than behaving solely as a surface coating.

The same general chemical affinity explains the traditional use of henna for temporary skin decoration. When applied to the skin, lawsone interacts with keratin in the outer layers of the epidermis and produces an orange-red to brown stain.

Skin Applications

Henna has traditionally been used for decorative body art and skin staining in many cultures. The practice has a history extending back thousands of years and has been documented in ancient Egypt and throughout parts of North Africa, the Middle East and South Asia.

The coloration results from the interaction of lawsone with keratin in the superficial layers of the skin. The resulting stain gradually disappears as the stained keratinized cells are shed.

Henna and lawsone-containing preparations have also been used traditionally on the skin in connection with minor wounds and various skin complaints. These historical uses should be distinguished from clinically established therapeutic applications.

Color Characteristics

Pure henna generally produces a warm orange, copper, auburn or reddish-brown coloration rather than a black color.

The final shade is influenced by the concentration of lawsone and the characteristics of the substrate. In hair, the resulting color is strongly influenced by the underlying hair color. On skin, the stain generally develops from orange to deeper reddish-brown over several hours following application.

The addition of other botanical materials can alter the final color of a henna preparation.

Formulation Considerations

Lawsone is naturally present in henna leaves and can be delivered through aqueous or other suitable extraction systems depending on the desired application.

Both water-soluble and oil-associated henna extracts have been described for cosmetic applications, although the chemical composition and coloring performance can differ substantially between extracts.

For hair-coloring products, the quality and concentration of lawsone are important parameters. Botanical source, harvesting conditions, processing, storage and extraction method can all influence the amount of available pigment.

The pH of the formulation and the conditions under which the product is applied can also influence the release and interaction of lawsone with keratin.

Stability

Lawsone and henna preparations can be affected by processing and storage conditions. Exposure to oxygen, light, heat and moisture can influence the stability and coloring performance of botanical preparations.

The stability of an isolated lawsone preparation may differ from that of a whole-leaf henna extract because the plant matrix contains numerous other compounds that can influence the behavior of the pigment.

Finished cosmetic products containing henna or lawsone should therefore undergo appropriate stability testing to evaluate changes in color, odor, appearance, viscosity, microbial quality and coloring performance.

Antimicrobial Properties

Lawsone and extracts of Lawsonia inermis have demonstrated antimicrobial activity in laboratory studies. Research has investigated activity against various bacterial and fungal microorganisms.

These findings may help explain some traditional uses of henna, but in-vitro antimicrobial activity should not be interpreted as evidence that a cosmetic product containing henna or lawsone can treat or cure a skin infection.

UV and Photoprotective Properties

Henna and other botanical extracts containing reactive naphthoquinones have been investigated for their interactions with keratin and their potential influence on UV absorption.

The interaction of lawsone with keratin produces colored compounds that can contribute to optical absorption. However, the presence of lawsone or a henna extract in a cosmetic formulation should not be interpreted as providing a validated sunscreen effect.

A product intended to provide UV protection must comply with the applicable regulatory requirements and be appropriately tested for its claimed level of protection.

Safety and Allergic Reactions

Pure, unadulterated henna has historically been considered relatively well tolerated, and adverse reactions to traditional henna preparations are uncommon.

However, allergic contact dermatitis has been reported following exposure to henna. The risk is particularly important with products marketed as “black henna.” These products may contain para-phenylenediamine (PPD) or other added colorants that are not naturally present in pure henna and can cause significant allergic sensitization.

The safety of a henna cosmetic ingredient therefore depends on the identity and purity of the raw material. Formulators should use appropriately specified, uncontaminated cosmetic-grade material and verify the absence of undeclared additives or adulterants.

Toxicological Information

Toxicological data for isolated lawsone should be distinguished from data relating to whole henna preparations or Lawsonia inermis extracts. The toxicological profile can vary depending on the test material, concentration and exposure route.

A specific NOAEL or LD50 value should only be reported when the underlying study clearly identifies lawsone or the relevant Lawsonia preparation as the tested material. Values from unrelated henna preparations or from adulterated “black henna” products should not be presented as representative of purified lawsone.

Traditional and Historical Use

Henna has been used as a natural dye for approximately 5,000 years. Historical evidence indicates that it was used in ancient Egypt for coloring hair, nails and skin.

Henna has also played an important cultural role in wedding and ceremonial traditions across North Africa, the Middle East and South Asia. Its use in decorative body art remains widespread.

Traditional accounts have also described the use of henna for hair conditioning, tired feet, minor wounds and various skin complaints. These historical uses form part of the ethnobotanical history of Lawsonia inermis but do not necessarily represent scientifically validated medical indications.

Regulatory Considerations

The regulatory status of henna and lawsone depends on the specific product, concentration, intended use and target market.

For cosmetic development, the botanical identity, plant part, extraction method and exact composition of the raw material should be documented. Particular attention should be paid to the distinction between pure henna and products marketed as black henna, which may contain additional chemical colorants.

Where lawsone or henna is used for hair coloring or skin coloration, the applicable cosmetic colorant and hair-dye regulations of the target market should be reviewed before commercialization.

References

Dweck, Anthony. Handbook of Natural Ingredients. Dweck Books.

European Commission. CosIng – Cosmetic Ingredients Database.

National Center for Biotechnology Information. PubChem – Lawsone.

National Center for Biotechnology Information. PubMed – Lawsonia inermis and lawsone.

World Health Organization. WHO Monographs on Selected Medicinal Plants – Lawsonia inermis.

Semwal, R. B., Semwal, D. K., Combrinck, S., and Viljoen, A. M. “Lawsonia inermis L. (henna): Ethnobotanical, phytochemical and pharmacological aspects.” Journal of Ethnopharmacology.

Al-Snafi, A. E. “A review on Lawsonia inermis: A potential medicinal plant.” International Journal of Current Pharmaceutical Research.

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