After getting a henna tattoo to celebrate my growing belly bump a few years ago, one person commented, "Oh, how beautiful, but isn't that bad for your baby?" I felt like being snippy and saying, "Yes, of course, it's bad for my baby. I like to do harmful things to my unborn child." But instead of being snarky, I explained that henna tattoos are completely safe for your skin, your body, and, yes, even if you're pregnant.
Also known as Mehndi, these tattoos are not permanent and only last between one and two weeks — depending on your skin, the quality of the henna, and how often you wash the area. The tattoo is applied in the form of a paste that looks like greenish chocolate frosting. It's made by grinding up dried leaves from the henna plant and is mixed with water, lemon, and essential oils. After the paste dries, it's peeled or picked off after about 24 hours, and you're left with an orangey-brown tattoo that stains the first few layers of your skin.
There is a trend among some henna artists to apply something called black henna, which will stain your skin black instead of brown. This type of henna is dangerous because it contains paraphenylenediamine (PPD), a hair dye. When applied to your skin, it may look like a real tattoo, but allergic reactions to PPD can cause blisters, open sores, and scarring.
It's easy to tell traditional natural henna apart from black henna. Traditional henna paste will look dark green, khaki, or greenish brown, not black, so if a henna artist is applying a slick black paste, then do not get a tattoo from her. You can also ask the artist how long you're supposed to leave the paste on. If she says less than one hour, then she's using PPD — traditional henna doesn't stain your skin that quickly. Also ask the artist what color the stain will be once the paste comes off. Henna will leave an orange stain that will darken to red brown or dark brown (like the photo above), but it's never black. If you're just not sure, then it's best to skip out on the henna tattoo or apply it yourself with a home henna kit.
Henna is one of the oldest and most popular ways to change your hair color, but for such a commonly used dyeing agent, there's comparatively little information around on why, how, and when henna is a good choice and when it isn't. If you're contemplating coloring your hair with henna instead of a peroxide or ammonia-based dye but don't know whether you're making the right decision, 
