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Henna experts agree that, yes, henna is safe for chemically relaxed hair, although you should always do a strand test first. Same goes for other chemically treated hair. The catch: the henna must be completely pure. Lots of impure mixtures are lurking out there, and they could frazzle your poor locks or leave them an icky green. The pure stuff will actually make your hair healthier, though.
How Henna Works
By coating each hair, henna seals and reinforces the hair shafts and pumps up the volume of hair. This gives hair a softer, healthier look and boosts shine, says Sandi Brenner in "Beauty and the Budget." Henna can actually relax your locks a little or make relaxed hair feel healthier, says Catherine Cartwright-Jones in "Henna for Hair." Henna will give African hair a subtle reddish cast or highlights, she adds. If you have brown hair, you'll probably get a brighter red color, which can get super intense as you use henna over time. Blondes should beware, since henna can make their hair orange. In other words, henna might help to repair your relaxed hair, as long as you haven't gone platinum blonde!
Choosing the Right Kind
Make sure you buy body art quality henna. Did you get that? Make sure you use only pure, body art quality henna over your relaxed hair. Steer clear of compound henna. Everyone with chemically treated hair should follow that rule to avoid disastrous results. If the box doesn't state the ingredients, drop it!
Precautions
Always do a strand test before dying all your hair with henna. That goes for people with completely natural hair, too. Take that big clump of stray hairs that built up in your hair brush, and test on it. Or, dye a small chunk of hair at the base of your neck. Follow the directions for your henna exactly, except preparing a smaller amount than you'll use for your whole head. Leave it on for several hours.
Getting Accurate Results
Henna's color can change over the next several days, so waiting a few days will give you a better idea of how your hair will really look with henna. Some henna proponents say they get a funky greenish cast at first, but it fades away within a couple of days.

