Some of you had questions about henna… so here are some answers!
Henna is the oldest known form of body art; its use can be traced back for at least 5000 years, and it is mentioned in the Bible as Camphire. All major world religions have henna traditions in their past, mostly centered around celebrations, and mostly applied to women (Buddhism and Judaism are two notable exeptions where men hennaed themselves).
Henna is a plant. The leaves are dried and ground to a fine powder, and mixed with lemon juice (or any acid), sugar, and, if you have some, monoterpene alcohols (found in things like lavender essential oil and tea tree oil). The acid in the lemon juice and the monoterpene alcohols begin a chemical reaction tht releases the natural dye, lawsone, from the henna leaf powder. Once you have dye release, you apply the henna paste onto your skin, usually using something that looks like a carrot bag.
Once you have the pattern drawn on your skin, you seal the paste on (I use medical tape), and leave it on as long as you can. I sleep in it. In the morning, take off the tape and the paste and you’ll most likely have a bright orange stain!
Henna stains the dead cells of your skin, but, as it is hydrophobic, does not stain the living cells. The bright orange stain will oxidize and mature over about 48 hours to a lovely deep walnut color, and after that, will remain on your skin until the cells that have been dyed naturally slough off… usually about 2 weeks. The henna, once it has dyed your skin, has the same properties as any other skin, and is completely waterproof, etc.
Henna is not black. What you see at beaches advertised as black henna is actually a chemical known as PPD, which is found in hair dye. The practice of using PPD as “henna” is illegal in all of Europe and the United States, though poorly enforced. PPD is usually as safe to use as any other serious chemical, but in some people it can cause life-threatening allergic reactions, and often causes a serious scar where the PPD was applied. Natural henna, on the other hand, is completely safe for everyone except for a few people (mostly Sephardi Jews) with a genetic disorder that also causes allergies to fava beans and moth balls.
Here are a few more pic of henna!