DO YOU KNOW

 How henna stains skin?

     Henna is a type of dye that's derived from leaves of the henna tree. When left on the skin, henna paste temporarily stains the skin a reddish-organge colour. It's used around the world to decorate the skin with intricate pattern and body art, known as mehendi, for celebrations such as weddings, birthdays and on festive occasions.

     To produce a dye, the dried leaves of the henna tree are first pulverised into a powder and mixed with a combination of oils or an acidic solution such as lemon juice. The resulting paste known as red henna can then be applied to the skin or hair to alter its colour. The change in colour is due to dye molecules in the henna tree's leaves called lawsone. When lawsone comes into contact with skin cells, it latches onto a protein called keratin, which holds onto the dye until the skin cells are naturally exfoliated away. Once the henna paste is applied, it typically needs to sit on the skin for several hours for the lawsone to penetrate deep enough through the skin's cellular layers to stain for a few weeks.

     Another additive called p-Phenylenediamine (PPD), an ingredient in hair dye, has been added in recent years to create 'black henna' in some parts of the world. However, the use of PPD has been made illegal in many places, including the UK and EU, because it poses a risk of causing severe skin reactions.

How far into the skin can henna penetrate?

[1] Henna paste: Henna is applied directly to the skin so the lawsone molecules can penetrate skin cells and bind to keratin molecules.

[2] Stratum corneum: This is the outermost layer of the skin's epidermis, where keratin-carrying cells called keratinocytes rapidly reduce.

[3] Deep saturation: When applied to the thickest layer of skin, found on the back or on the hands, lawsone can penetrate 30 cell layers deep.

[4] Granular layer: Henna doesn't penetrate into the granular layer, which acts as the skin's impermeable barrier against water.

[5] Basal layer: The innermost layers of skin, where new protective keratinocytes are produced.

Ancient origins: The exact origins of henna are difficult to determine. There's evidence of the dye being used in early Babylonian civilisations from around 1894 to 539 BCE and during the time of ancient Egypt, between 3100 and 395 BCE. Henna was used to decorate the bodies of the deceased, and in some cases on the strips of linen wrappings used for mummification. Much like the keratin found in hair and nails, lawsone is resistant to decay and remains on the body after death. When archeologists examined the remains of the Egyptian pharaoh Ramesses II, also known as Ramesses the Great, they discovered that his hair, while white at the point of his death, had been stained bright orange with henna.