To understand low porosity, you need to understand porosity in general. Porosity refers to your hair’s ability to absorb and retain moisture. The level of porosity can determine how much water and other products are able to penetrate your hair and scalp. As Dr. Karen Kagha, a board-certified dermatologist based in California previously explained to us: “The hair cuticle plays a role in the porosity of the hair because it acts as a protective barrier to the hair shaft,” before adding that “the cuticle can be damaged by heat, over-manipulation or chemicals, thus altering the hair’s porosity.”

When it comes to low pollution hair, water and other substances have a harder time penetrating your hair. Your cuticles are tighter, so products tend to sit on top of your hair, which can lead to dryness, breakage and tangles. Note: If you need help figuring out your own hair porosity, the water test is your best bet.

To do this, simply grab a glass of water, gather a few strands and drop them into the water. Watch how your hair reacts to a little H2O. If it floats to the surface, you have low porosity hair; have high porosity hair. And if it stays in the middle of the glass, you more than likely have medium to normal porosity.