Hair serums put to the test: Which is best?

Why it's unique: Ecru New York Acacia Protein Oil is packed with natural botanicals (including its namesake, an extract from the African acacia tree, as well as apricot-kernel and argan oils), all of which seal in moisture. It's perfect for protecting hair from heat styling.Tester's take: The Ecru formula is extremely light, and doesn't weigh hair down at all. I used it on dry hair—rubbed a dime-size amount between my palms—and it added a high-wattage shine. It also smells great; it has a fresh, slightly fruity scent.SHOP NOW: Ecru New York Acacia Protein Oil, $30

Why it's unique: Bumble and Bumble Hairdresser's Invisible Oil is extremely light and imparts more softness than shine. Perfect for those with thin hair that's easily weighed down, this silicone-based treatment also provides UV protection.Tester's take: The consistency was thinner than other hair oils I've tried. It worked best when I applied it on wet hair and then blew it dry. The shine it added was very subtle. The scent was subtle and woodsy.SHOP NOW: Bumble and Bumble Hairdresser's Invisible Oil, $32

Why it's unique: SachaJuan Intensive Hair Oil is a creation of one of Stockholm's top salons. Its botanical ingredients include argan and sea-buckthorn oils. It's quickly absorbed, making it a great choice if you are looking for increased manageability over a glossy look. Tester's take: It's good at taming flyaways and making hair softer. But, whether or not you're a fan of this product all comes down to the scent. It's a very strong, almost unisex smell. If it appeals to you, you'll love it. SHOP NOW: SachaJuan Intensive Hair Oil, $45

Why it's unique: Matrix Biolage Exquisite Oil Replenishing Treatment is for use on all hair types—from color-treated and damaged to thick and frizzy. Its formula—including macadamia-nut oil and argan oil—is on the thick side, and it imparts an intense sheen. Tester's take: I loved it! It made my hair super-shiny. I have thick, sometimes coarse hair and this smoothed it down well without making it greasy. I would definitely buy it.SHOP NOW: Matrix Biolage Exquisite Oil Replenishing Treatment, $14

Why it's unique: This non-greasy, alcohol-free formula gives a lot of bang for the buck. It is on the thicker end of the smoothing-product spectrum and delivers major shine with just one or two pumps.Tester's take: I adore this serum. I have color-treated hair that tends to be dry and dull. But just a small amount, lightly applied to dry hair, gave me a definite sheen without being at all greasy. It also smells rich and nutty.SHOP NOW: L'Oréal EverStyle Smooth & Shine Serum, $6

Why it's unique: Global Keratin Hair Taming System Serum contains a proprietary ingredient called Juvexin. Derived from sheep's wool, Juvexin is purported to coat the hair shaft, keeping it moisturized and soft during styling.Tester's take: This product tamed and controlled the frizz in my hair. I found that it worked better if I applied to damp hair before blow-drying. The shine and softness lasted all day. I also applied a tiny bit more before going out—to dry hair—and it freshened it up.SHOP NOW: GK Hair Taming System Serum, $25

Why it's unique: Simply put, this Oscar Blandi serum smells wonderful—natural extracts of jasmine ensure that. The formula also includes sweet almond oil and vitamin E oil to moisturize and protect hair from heat. Tester's take: I really liked the smell, it was light and so pretty. It gave my hair a great shine without weighing it down. It's the perfect post-blow-out product.SHOP NOW: Oscar Blandi Olio di Jasmine Hair Serum, $16

Why it's unique: Caudalíe Divine Oil can be used to moisturize the hair and body. Made of 60 percent pure vegetable oils and scented with fresh Moroccan and Bulgarian rose extracts, it's a lovely French indulgence.Tester's take: It has a spray applicator that really helps keep the application light. I usually put on too much product when it comes to oils, so I love this. I absolutely love the scent, and the bottle is so pretty I keep it on display in my bathroom!SHOP NOW: Claudalíe Divine Oil, $45

Why it's unique: Tigi S Factor True Lasting Colour Hair Oil uses micro-fine moisturizing components—including silicone and coconut and sweet-almond oils—to penetrate the hair's cuticle. The result is an all-day shine.Tester's take: It made my hair very shiny and sleek and soft! It smells lightly floral and was quite pleasing—I even dotted some behind my ears with the leftover amount on my palms.SHOP NOW: Tigi S Factor True Lasting Colour Hair Oil, $24

Why it's unique: Beauty pros have been known to call Shu Uemura Essence Absolue Nourishing Protective Oil liquid gold. It can be used as a pre-shampoo moisture mask and an overnight treatment in addition to serving as a frizz-buster.Tester's take: It didn't weigh my hair down at all, rather it left it lovely and shiny. It got rid of flyaways on the top of my head and made the bottom of my hair sit beautifully. No scent at all which was really nice. I don't like it when beauty products compete with my perfume.SHOP NOW: Shu Uemura Essence Absolue Oil, $68