The 9 Best Deep Conditioners, Tested by Cosmo Editors With All Hair Types

Deep conditioner (often called a hair treatment or hair mask) is used for moisturizing, smoothing, and repairing hair, depending on the formula you choose. Unlike traditional rinse-out conditioners, deep conditioners tend to have super-high concentrations of moisturizing ingredients (like avocado oil, castor oil, shea butter, jojoba oil) and strengthening proteins (like amino acids, keratin, silk, vegetable, etc.).

Deep conditioners are also packed with conditioning surfactants that stick to your strands and act as a sealant to prevent water loss, while also penetrating deep into your strands to hydrate. Though these agents are commonly found in everything from shampoo to heat protectants, they’re especially high in your deep conditioner, because deep conditioners “are formulated to coat your hair fiber while also tightly flattening the scales of your cuticle,” says Hill.

How often you deep-condition your hair will depend on your hair type and how damaged or dry your hair is. Those with dry or coarse hair (regardless of damage level) can—and should!—use a moisturizing, protein-free deep conditioner every week (or every other week for fine hair), then incorporate a protein-filled deep conditioner once a month.

The important rule to keep in mind is “moisture over protein,” meaning when in doubt, load up on the protein-free formulas as often as you want, and save the protein-heavy formulas for once-monthly treatments.

How long you leave your deep conditioner in your hair will change depending on the specific product you’re using. A moisture-based deep conditioner can stay on your hair for any amount of time, from five minutes to 30 minutes to overnight, says Hill. But “protein-based deep conditioners can have a negative impact on your hair fibers if left on too long.” So you should always check the packaging directions for your deep conditioner for the recommended time.

All hair types can benefit from deep conditioner (yes, even fine, thin hair), but you’ll need to look at the formulation to see if it’s right for your hair type to get the best results. “If your hair is chemically altered, whether by hair color, highlights, or straightening or perming chemicals,” says Hill, “or if you have hair that’s coarse, curly, or tightly coiled, you can benefit from a rich, moisturizing deep conditioner.”

Fine hair types, however, or hair types that have a low porosity (meaning products tend to build up on strands and weigh them down) should opt for lightweight deep conditioners with minimal amounts of heavy oils and butters. Generally, the thinner the formula, the lighter it tends to be, so look for deep conditioners in spray bottles, pouches, and pumps rather than in jars, and go for packaging that has words like “milky,” “water,” “rinse,” and “gloss.”

That being said, you won’t ruin your hair if you use a too-heavy deep conditioner on fine hair, or a too-sheer formula on damaged hair—you can always rinse it out or layer more on. The most important factor to remember is protein; too much protein will mess with your hair, so it should be top of mind. Which brings us to…

Figure out what your hair needs

Is your hair actually damaged, or is it just dry? Like, has your hair recently been bleached, chemically treated, or subjected to daily blowouts, flat irons, or curling irons? Then it’s probably damaged (more on this below). But if your hair is dry, tangled, rough, and unhappy—even though it’s rarely subjected to any heat tools or damaging treatments—then you’re probably dealing with dry hair that’s in desperate need of a ton of moisture, specifically a protein-free deep conditioner.

But if you can confidently say that your hair is super damaged, look for a deep conditioner with protein, which will help seal the holes in your damaged hair cuticle to give it strength and structure. Our faves we tested were the Mielle Babassu & Mint Deep Conditioner and Olaplex No. 5 Bond Maintenance Conditioner. “When you damage your hair with chemicals, heat, chlorine, or chemical treatments, you need to replace some of the protein that is lost,” says Friese. But here’s where it can get tricky because...

Consider the protein levels

Usually, if your deep conditioner has any anti-breakage lingo on the label (Strengthens! Restores! Repairs!), you can bet it’s packed with proteins. But here’s the important part: Too much protein will make your damage, dryness, and breakage way, way worse—especially if your hair didn’t actually need protein in the first place (see: regular ol’ dry hair).

When you use too many anti-breakage products, protein quickly builds up on your hair strand like a stiff, suffocating shield, drying out your strands until they turn brittle and break off. Not good. So if you’re already using a “restorative” shampoo and a “damage-repairing” conditioner every shower and then you slather on a “strengthening” deep conditioner that’s loaded with protein, you’re playing a game of risk. Instead, incorporate low-protein and protein-free deep conditioners in your arsenal too, like Color Wow Money Mask Deep Hydrating & Strengthening Hair Treatment and Davines The Renaissance Circle.

• Bridgette Hill is a certified trichologist and founder of Root Cause Scalp Analysis, a virtual platform that offers personalized scalp analyses and treatment plans.
• Gretchen Friese is a hairstylist and trichologist consultant with BosleyMD. Friese is also the founder and salon director of Foushee Salon in Littleton, CO.

Beth Gillette is the beauty editor at Cosmopolitan with five years of experience researching, writing, and editing hair stories that range from blue hair to hair botox. She’s an authority in all hair categories, but is an expert when it comes to pimples around your lips after a decade of dealing with acne. She regularly tests and analyzes deep conditioners for efficacy, while working with the industry’s top dermatologists to assess new formulas and brands.