Henna, lawsonia inermis, is a plant. It is a large bush, or small tree, that grows in hot, dry climates. There is evidence from Egypt that henna was regularly used to dye hair five thousand years ago, and may have been used in Jericho as early as eight thousand years ago. Henna was used to keep hair healthy and to color gray hair.
Henna leaves are harvested, dried, and powdered. When mixed with a mildly acidic liquid, henna will stain skin, hair, and fingernails reddish-orange.
Henna´s leaves have a red-orange dye molecule, lawsone. You can see it in young leaves in the center vein of the leaf. Henna leaves have 1% to 4% lawsone content, depending on climate and soil conditions. The lower dye content leaves are harvested, roughly powdered and sifted, and sold to the hair dye industry.
The highest dye content henna, the best 5% of the crop, is powdered and finely sifted to make design on skin, such as are used for celebration in North Africa, in the Middle East and South Asia. This is body art quality (BAQ) henna. Body art quality henna is wonderful for your hair because the fine powdering and sifting make it rinse out easily, and will dye hair a richer color.
Mention of henna can be found already on Ebers papyrus from ancient Egypt dated to the year 1500 BC, however, it is believed to have copied from earlier texts, perhaps dating as far back as 3400 BC. Among the some 700 magical formulae and remedies, a detailed coverage was dedicated to henna as tribute of the complexity of the product and its plant, lawsonia inermis.
From ancient Egypt and neighbor countries, the use of henna has continued for thousands of years in Arabian countries and nowadays it is expanded all over the world. The main use is cosmetic, to dye hair and nails and for decorative bodypainting. However, the use of hair dyes has dramatically increased during the last decades.
Types of henna
Several types of henna are on the market: commercial red henna is based on Lawsonia inermis, black henna on Indigofera tinctoria, neutral henna on Cassia obovata and blond henna on Cassia obovata with addition of several other plants.
The coloring action of red henna is usually due to lawsone, present in the leaves together with its glucosides (hennosides). In the dried leaves, besides lawsone (0,5 – 2 %), other compounds are also present, co-occurring in the activity as well as in characterization of the raw material like polyphenols (flavonoids, gallic acid) and glucides. Henna is considered safe, although one study claimed that the application can induce a severe haemolytic anaemia and may contribute to neonatal hyper bilirubinemia. However, a real toxicity for henna should be excluded on the basis of investigation on large populations and on consumers of professional exposures.
The lawsone position is different. Its content has to be checked and essayed for its potential toxicity because some cases of renal damage and bladder cancer have been reported. Thus, in EU the content of lawsone in cosmetic preparations must be avoided and limited to 1,5 % in products based on Henna and declared in the label.
However, most of the quality problems are related to the plant ingredients: henna can contain fruits and twigs, as well as parts of other plants. The aim of the addition of other plants or natural or chemical substances could be the modification of the hair color or to improve the penetration or the fixing of the dye or to reinforce the hair color or to improve the hair protection, effects given by a lot of associated additives, from keratin to heavy metals. Actually, natural henna has very law allergic potential, and allergic reaction are caused by the chemical coloring additives that are added to henna mixtures to improve or modify dyeing. Several products marked as henna do not contain any natural constituent or only in law quantity.
How to know the compound henna
Studies in Natural Products Chemistry – Atta – ur – Rahman – Volume 37 (svazek)
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