Does your hair take forever to dry? Or maybe it seems like when you apply products, they seem to just sit on top without absorbing? Both are related to hair porosity, which can affect everything from washing to styling. Here's what makes hair porous and why it matters.

The science of how your hair behaves is complicated, but hair porosity has a pretty simple definition: how much water your hair can absorb.

The cuticle is the outside layer of your hair strand, and it's made up of overlapping cells, similar to shingles on a roof. These can let moisture in, and conversely, keep water out - depending on how porous your hair is.

Your natural porosity is hereditary. Other factors can contribute to porosity over time, which is why the hair near your scalp might not have the same porosity as the ends. Porosity increases when the hair cuticles experience damage, making them less able to protect the strand. Water can then more easily move in and out of the hair.

Chemicals, exposure to sun, heat styling and rough rubbing or brushing can all cause this type of damage.

Low porosity hair tends to be shinier, less frizzy and holds onto hair color better. Because it doesn't allow moisture in as easily, low porosity hair can be harder to moisturize. Often, people with darker hair have lower porosity.

High porosity hair tends to be less smooth, more stretchy and more prone to breakage. It takes longer to dry, but responds better to moisturizing treatments. Often, lighter hair is more porous.

You can't reverse high porosity once damage is done, but you can combat the effect of high or low porosity. For hair with low porosity, it takes more effort to add moisture, but once it's there, it usually lasts longer. Apply a treatment, like Shu Uemura Moisture Velvet Nourishing Treatment Masque For Dry Hair, and let it soak in before washing. Follow with a leave-in conditioning treatment, like SoftSheen-Carson Dark and Lovely Healthy-Gloss 5 Moisture Leave in Treatment or Kiehl's Damage Repairing & Rehydrating Leave-In Treatment.

Highly porous hair tends to respond quickly to conditioners, but the effects don't last as long. Make hair feel and look smoother with a gentle shampoo like Pureology Purify Shampoo, and protect from heat styling with a product like Matrix Total Results Heat Resist Iron Tamer Smoothing Lotion. For very damaged hair, try something like Redken Extreme Anti-Snap / Distressed Hair Treatment. Consider velcro rollers instead of a high-heat daily blowout.

Can you tell if your hair is more or less porous? Tell us how in the comments below!

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