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If you're looking for a magic oil that'll grow your hair overnight, you've probably come across some pretty convincing testimonials of black seed oil (aka Nigella sativa, aka black cumin). As you can tell, the ingredient's got a lot of different names, and some people even consider it a straight-up godsend for any number of hair struggles (think: fine or finning hair, dullness, dryness, the works). But because you can't believe everything you read on the internet (I've definitely made that mistake once or twice and totally paid the price), I turned to board-certified dermatologist Dhaval G. Bhanusali, MD, to figure out what black seed oil can really do for your hair (and, you know, what it can't).