This could be why your hair products aren't working

When it comes to healthy hair, knowing your hair type—that is, whether it’s straight, wavy, curly, or coily—is only half the battle. There's another characteristic at play, and it’s your hair’s porosity, or how well your strands are able to absorb and retain moisture. Understanding hair porosity is important for everything from product selection to styling, and can save you from experiencing a slew of frustrating hair dilemmas, including styling difficulties, lack of results from hair products and, in some cases, hair damage.

To learn all about hair porosity—including the different types and how to test yours at home—we spoke with Ireland-born celebrity hairstylist Andrew Fitzsimons and hair colorist Aaron Bradford of Cédric Salon in NYC.

What is hair porosity?

Your hair structure is made up of three layers: the medulla (the innermost part of the hair shaft), the cortex (the thick, middle layer), and the cuticle (the outermost part of the hair shaft). "In order for your hair to stay hydrated and healthy, water, oils, and other moisturizing agents have to pass through the cuticle to get to the cortex," says Fitzsimons. Depending on your hair's porosity, it can be difficult for your hair to facilitate this passage of moisture and thus be as healthy as it can be. Knowing where your strands stand on the porosity spectrum can help you tailor your routine accordingly.

There are three main categories of hair porosities: low, medium, and high. The lower the hair porosity, the more difficult it is for moisture to transfer into the hair, says Bradford. On the other hand, hair that's high in porosity is more likely to lose and acquire moisture easily.

How to test hair porosity

You don't have to pay a visit to your hairstylist to figure out what your hair porosity is—a simple at-home water test will do the trick. To do the test, you'll need a glass of lukewarm water and freshly washed hair strands to ensure there's no product buildup, which can affect your results, says Bradford. After washing your hair, brush your hair to collect the shedding strands for the test (please—don't pull out a hair for this!), and after they've air-dried completely, place a few on top of the water in the glass. After five minutes, your hair will do one of three things: float (signifying low porosity hair), sink very slowly to the bottom or suspend in the water (signifying medium porosity hair), or sink immediately (signifying high porosity hair).

Another way to test your hair porosity is to slide your fingers up one strand of hair from the end toward your scalp. "If you feel roughness, this means your cuticle is lifted and you have high porosity hair. If your fingers glide evenly, then you have low porosity hair," says Fitzsimons. If it feels smooth with slight texture, you have medium porosity hair. This may be more difficult to discern if you have a finer hair type, but those with coarser hair may find it another effect test.

What is low porosity hair and how do you care for it?

"Low porosity hair is characterized by tightly sealed cuticles that restrict the hair from acquiring moisture from external sources," explains Bradford. "If not addressed, this may lead to product buildup and a dry, dull texture that's susceptible to breakage." Some characteristics of low porosity hair are greasiness on account of products being unable to soak in, difficulty saturating your hair in water, and long drying times post-shower. Low porosity hair may also not take color or bleach well, as it's more difficult for the chemicals to penetrate.

If you have low porosity hair, look for products that are lightweight or made for oily hair. If your hair is prone to buildup, incorporate a clarifying shampoo into your routine one to two times a week. A good one to try is the Ouai Detox Shampoo, which uses apple cider vinegar to cleanse away dirt, oil, and product buildup. Also, to open up the cuticle and deposit moisture before styling, Bradford recommends throwing on a shower cap after you’ve rinsed out your shampoo and conditioner—this will trap in body heat and shower steam to help open up the cuticle. Finally, if you'll be heat styling your strands, apply a water-based leave-in conditioner, like the fan-favorite Mielle Organics White Peony Leave-In Conditioner, before applying your heat protectant to amp up the moisture.

What is medium porosity hair and how do you care for it?

This is the most balanced of porosity types where the cuticle is neither tightly sealed nor flared open, and it easily invites moisture in. Medium porosity hair is easy to style, takes color well, tends to look healthier and shinier, and doesn’t take long to air-dry, says Fitzsimons. That being said, medium porosity hair is susceptible to becoming highly porous through excessive heat styling and coloring, Bradford says, so it’s important to be mindful of the products you use in order to maintain a healthy porosity level. Medium hair porosity can follow a basic hair care routine for normal hair that consists of a leave-in conditioner and a heat protectant (if heat styling), followed by a hair oil like Moroccanoil Treatment Oil, which helps if you have breakage or dry hair, thanks to a blend of argan oil and linseed extract. You can also use a clarifying shampoo bi-weekly to remove product buildup along with a deep conditioning mask weekly for overall scalp and hair health, says Bradford. A mask with rave reviews is the It's a 10 Miracle Hair Mask—it's a gentle yet powerful deep conditioning mask that leaves hair smooth, detangled, and hydrated.

What is high porosity hair and how do you care for it?

If you have high porosity hair, your cuticles are flared open, which allows for moisture to pass in and out easily. While you may notice that your hair air-dries quickly, high porosity hair is more susceptible to frizziness, dryness, dullness, breakage, and tangling, says Bradford. "Because the cuticle is so open and flared, the hair strands don’t lay orderly on top of one another—instead, they hook into one another, which causes them to repel one another and make them more vulnerable to the aforementioned quandaries."

High porosity hair craves moisturizing products, so anything labeled “for dry hair” is a good place to start. Apply your styling products onto wet hair to trap in as much moisture as possible, recommends Bradford. To lightly blot your hair, use a microfiber cloth rather than a traditional terry cloth towel, as these are more gentle on the strands, create less friction, and are less likely to pull or tug on the hair. "Depending on how fragile your hair is [i.e.: if it's fine and prone to breakage], consider an ergonomic wet brush with flexible bristles—this will prevent breakage because the bristles bend once they encounter too much resistance." Lastly, swap your everyday conditioner for a deep conditioning mask for extra hydration. A good one to try is Eva NYC's Therapy Session Hair Mask, which has rave reviews for its ability to smooth dry, damaged strands with argan oil and essential vitamins. Sleeping with a lightweight cap wrapped around your head can also help minimize breakage as you toss and turn. Try the Grace Eleyae Satin-Lined Sleep Cap, as it’s lined with satin to protect your hair from pulling and hold in its moisture.