Recently the FDA announced that black henna temporary tattoos may result in burns and scars on the skin. But the "henna" products which cause these reactions have chemical additives, and are not a pure plant product. Many prepackaged hennas contain other botanicals, synthetic dyes, and sometimes dangerous compounds, such as PPD (para-phenylenediamine) which can cause severe blistering.
There is only one "true" henna (lawsonia inermis) which is often referred to as "red" or "rajah" henna. Rajah henna powder is used to tint the hair, to dye textiles, and for Mehndi - a "temporary tattoo" body art practiced mainly in India and Nepal. organic hibiscus powderWomen use it to put decorative patterns on their skin, mostly the hands and feet, in preparation for special events such as traditional Hindu weddings. When using it as a hair color, it permanently binds with the hair and the color becomes richer with repetitive use. Henna is also an excellent conditioner that improves the health of the hair.
Two plants that are used in a similar way as true (red) henna, which include black "henna" (Indigofera Tinctoria) and neutral "henna" (Cassia Obovata.) Black henna is used the same way as red henna, but stains black instead. Cassia is primarily used for its conditioning and antimicrobial properties, but can also enhance tones in blonde hair.
When mixing henna for a hair dye, you must add something acidic such as lemon juice or apple cider vinegar to activate the dye. To enhance the dye production, add essential oils of tea tree, cajeput, or ravensara. Other essential oils can be used for this purpose, but these three seem to work best. For the liquid to mix with the henna powder, you can brew a tea (choose hibiscus to enhance the red tones) or simply use warm water. Add liquid until it becomes a yogurt-like consistency. You can get creative and add other things to the mixture, such as beet root powder, cinnamon, nutmeg, coffee, etc. to make a custom blend. When the henna has turned a dark shade of brown, the dye has released and you can now apply it to the hair (remember to use rubber gloves!) Cover hair with plastic wrap and/or a towel, and leave it on for a minimum of four hours, or overnight. Using heat, such as a blow dryer, can expedite the process. If you want to condition the hair without changing the color, only leave the henna in for a short time, or just use the cassia/neutral henna. Mixing henna for skin is a very similar process, but it should be made into a thicker paste, like the consistency of mashed potatoes. You can apply the henna with a bottle or an icing tube.
If you want a clean natural product to color and nourish your hair, or if you want to indulge in some temporary body art, real natural henna products are a great choice. Use caution to make sure the henna products you purchase do not contain additives and chemical.