We love to divide hair into categories: Thick or thin? Curly or straight? Dark or Light? But there is one distinction that has flown under the radar for too long: High porosity or low?
Porosity dictates how absorbent your hair is, due to the gaps and breakage on the strands themselves. High-porosity hair is extra absorbent and often somewhat damaged, soaking up water and conditioning products like a sponge — then drying out just as quickly. Hair with low porosity has a tightly-sealed cuticle (aka outer layer) and often fails to absorb conditioners and styling products, gathering buildup.
“If you think of hair that’s dry and frizzy, and most likely curlier, that hair tends to be porous,” says New York City stylist and salon owner Nunzio Saviano. “If you see thick, straight hair that’s been dried naturally and is shiny, the porosity is low.”
While hair porosity levels are mostly genetic, it can vary based on a number of factors: hair treatment, color processing, hard water and even the weather. We tend to think of cold, winter air as particularly drying, but summer brings its own set of problems. “If you’ve been at the beach all week, if you’ve been in the sun and been swimming, [your hair is probably] extra porous,” says Saviano. The same goes for hair that is bleached or regularly heat-treated.
“There’s a huge benefit to knowing one’s hair porosity because it helps you choose products and styling tools,” adds editorial stylist Clay Nielsen. “Different porosities have different needs.” Here’s how to tell what they are.
Knowing one’s hair porosity helps you choose the right products and styling tools.
How to tell your hair’s porosity
Your hairstylist should be able to give you a quick diagnosis at your next appointment since they likely have experience treating all levels of porosity. But for a DIY approach, try a float test. Pluck a stray strand from your hairbrush, or off your shirt, then fill a bowl with water. Drop your strand in the water and watch what happens. If the strand floats for a while before slowly sinking, it is a sign your hair has low porosity. If the strand drifts to the bottom, your porosity is likely normal. But if the strand makes a crash-landing to the bottom of the bowl, taking on water like the Titanic, that signals high hair porosity.
The surest sign that high-porosity hair is closer to normal, says Saviano, is elasticity. “Your hair should bounce,” he adds. Curls will spring back into place and hair will move when you walk. You might also notice that your hair soaks up less conditioner in the shower and doesn’t feel quite so dry. But since porosity almost always has some genetic component, the results won’t last forever (with the right upkeep, dry, dull, breakage-prone hair can truly shine).
Another way to tell is by simply paying attention. “If you add a dime size of conditioner and your hair really sucks it up,” that is a sign you are dealing with high porosity, says Saviano. If the lightest touch of the hydrating product leaves you looking like an oil slick, on the other hand, your hair likely has low porosity, and might need a little help absorbing products.
How to treat and style high-porosity hair
Is your hair feeling particularly thirsty? Ditch drying products. “I tell people with high porosity hair to avoid shampoos, as they’re often abrasive and will open the cuticle more,” says Nielsen. “A co-wash, like New Wash from Hairstory, is a great option for a cleanser.”
Once the hair is clean, focus on adding back lost moisture. If the hair is damaged, opt for a moisturizing treatment made specifically for hair that needs both moisturizing and repairing, such as Aveda Damage Remedy Intensive Reconstructing Treatment, suggests Nielsen, to “help restore the bonds and nourish the hair to prevent future damage.” Then, he likes to seal hair with a swipe of a styling iron (like a T3 Singlepass) at low heat — it is not hot enough to damage hair, just to smooth the cuticle and stop moisture from seeping out of gaps.
And don’t be afraid to layer on the conditioner, says Saviano. He suggests his own Hyaluronic Hair Repair and Replenish, which uses hyaluronic acid to help retain moisture. “Most women think that by adding a little more, it’s a negative thing, but it’s a positive thing. If your hair’s asking for more condition, you should use a little more.” If you overload and feel like you are weighing your hair down, you can always rinse it back out again. Or, try an overnight leave-in conditioner, such as Kerastase 8H Magic Night Hair Serum.
It is also worth reevaluating your styling routine. “Misuse of chemical treatments are often the leading cause of damaged hair,” says Nielsen. If salon straightening treatments or color processing leaves your hair parched, seek out another stylist.
And if you are a blow-dry addict and worry that you are overdoing it, says Saviano, “take a step back and reduce the amount of heat styling.” Leave the heated tools to special events and keep blow-drying to a minimum.
How to treat and style low-porosity hair
While hair with low porosity is typically less damaged than high-porosity hair — and may seem perfectly healthy — it comes with its own set of issues. “Penetrating the cuticle can be difficult with low porosity hair,” says Nielsen. “After applying conditioner, I like to wrap the saturated hair in a [cotton] towel and blow-dry the towel with my T3 Cura Blowdryer. The towel will keep the heat trapped in and allow the cuticle on the hair shaft to open up and absorb the nutrients from the conditioner.” Finish by rinsing hair with cool water and air-drying for maximum shine.
If your low-porosity hair feels dull, greasy or weighed down with products, look for a clarifying shampoo that cuts buildup, like Ouai Clean Shampoo. It is a little more stripping than your average wash but can remove oils and conditioners that aren’t absorbed by the hair. For a natural option, try rinsing hair with a mixture of apple cider vinegar and water.
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