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Organix Coconut Milk Anti-Breakage Serum, $6.99
Silicone is the double-edged sword of hairstyling. Nothing beats it for blocking out the humidity that creates frizz—yet it can quickly become too much of a good thing, making hair lank and greasy. This serum harnesses silicone's frizz-fighting power but is so lightweight that it's almost impossible to overdo. A couple of squirts smooth even fine hair without weighing it down.