Hair Porosity: What It Is, How to Test It, and High vs Low Porosity Hair

Most porosity advice treats it like eye color: a type you were born with, found by dropping a strand in a glass of water. In hair that has been colored, lightened or heat-styled, it usually works the other way. Porosity builds up from root to tip, and you can read it yourself with a spray bottle. Mist the hair nearest your scalp, then your ends. If the roots bead and the ends soak the water in, the difference is damage, and where it starts may tell you when it happened. Below is how to run that test properly, what the float test really measures, and when your hair needs no repair at all.

What is hair porosity?

Hair porosity is how easily water and products move into and out of a hair strand. It is set by three things: a water-repellent film on the surface, the overlapping scales of the cuticle beneath it, and the inner structure of the fiber. Sealed and flat means low porosity; stripped, lifted or chipped means high porosity, which in colored or bleached hair usually signals damage.

Porosity is less a type you are born with than a record of what your hair has been through.

Low, medium and high porosity at a glance

Low, medium and high porosity hair compared

	Low porosity	Medium porosity	High porosity
Surface and cuticle	Water-repellent surface intact; scales flat	Mostly intact; some wear toward the ends	Surface stripped; scales lifted, chipped or missing in places
Water misted on clean, dry hair	Beads and sits	In between	Spreads and soaks in
Feel, compared with the hair at your scalp	The same from root to tip	Slightly rougher toward the ends	Clearly rougher; tangles more
Conditioner	Binds less of it; a little is enough	A moderate amount	Binds it strongly; needs it every wash
Most common reason	An intact fiber: new growth, or hair rarely colored, heat-styled or sun-exposed	Ordinary wear: washing, brushing, sun, time	In colored, bleached or heat-styled hair, accumulated damage; in untreated hair, fiber shape and wear
What it needs	Less, and protection	Maintenance and protection	Stop the cause, then treat the surface and the core

Test your roots and your ends separately. Colored hair is often low or medium near the scalp and high at the ends.

Not sure which column is yours? The ANATOMY hair porosity quiz asks a few questions about color, heat, washing and how your hair behaves, then scores your porosity (low, balanced or high) and any damage, and gives you a Damage Profile with a routine matched to it. It is free, takes about a minute, and asks for your email before it shows your result.

Find your porosity with the free quiz

Inside the strand: surface, scales and core

Picture a single strand as a rope wrapped in roof shingles. The rope is the cortex: bundles of keratin protein, cross-linked by sulfur-to-sulfur (disulfide) bonds, that carry almost all of the load when hair is pulled. The shingles are the cuticle, typically six to eight layers of flat, overlapping cells. The shingles have a finish, a layer one molecule thick of a fatty acid called 18-MEA, and it is the main reason water beads on healthy hair (Robbins 2012). Porosity rises as that system opens up: the finish comes off, scales lift and chip, and broken bonds leave spaces inside.

How to test your hair porosity at home

The simplest hair porosity test is a spray bottle and a comparison. Mist clean, dry hair with plain water. Droplets that bead and sit point to a sealed surface: low porosity. Droplets that spread and soak in point to a stripped surface: high porosity. Test your roots and ends separately; if only the ends soak in, the difference is damage.

The first inch or so at your scalp is the youngest hair you have, and hair cannot repair itself, so the damage done to a strand stays in it (Robbins 2012). Unless your roots are colored, they are your control.

Does the float test work?

Not as a porosity test. The float test, where a strand that sinks in a glass of water is called high porosity, mostly measures surface tension. Hair is about a third denser than water, and bleaching barely changes that (Robbins 2012), so every strand sinks eventually. How long it floats depends on surface oils, product residue, how you drop it and how long you wait. We found no peer-reviewed study that validates the float test. A post on the New York Society of Cosmetic Chemists blog is more generous, and applies the same caution to the spray test used here: simple methods like these "have limitations but can potentially give a general idea under controlled conditions" (Evans 2020).

So if your hair floats in water, it is not necessarily healthy. It may simply be coated.

Before you start: clean hair and your history

Wash with a plain shampoo and skip conditioner, leave-in, oil and styling products. Residue makes damaged hair act healthy: in one lab study, a conditioner brought bleached hair back to the water repellency of untreated hair (Liu 2022). Let your hair dry completely.

Then note what your hair has been through, which is often a better guide than any kitchen test:

• whether any part has been lightened or permanently colored, and where that part begins
• whether you use a flat iron or curling iron, and ever on hair that is not fully dry
• how long it is: the ends of shoulder-length hair are often two years old or more
• how much strong sun it has seen

If you have lightened recently, the spray test may flatter your hair. Bleaching alone does not remove all of the surface's water repellency; washing and wear finish the job (Tokunaga 2019). Recently lightened hair can still bead water for a while, even though the damage inside is already done.

Step 1: The spray test (the surface)

1. Take a section of clean, dry hair and hold it flat between your fingers.
2. Mist the part nearest your scalp with plain water from about 8 to 12 inches (20 to 30 cm) away.
3. Watch for half a minute. Do the droplets sit as beads, or spread and darken the hair?
4. Mist the ends of the same section the same way and watch again.
5. Repeat on two or three sections from different parts of your head.

Beading means the water-repellent surface is largely intact: low porosity. Spreading means much of it has gone: high porosity. In one lab study on bundles of hair, water met untreated hair at an angle of about 97 degrees and bleached hair at about 62 (Liu 2022), the difference between a round bead and a flat drop that soaks in. The test reads the surface only, and there are no validated timings. What matters is how your roots compare with your ends.

Step 2: The slide test (the scales)

Hold a single strand at the scalp end and slide finger and thumb slowly from the tip toward your head. Every hair feels a little rougher in this direction, because the scales all point toward the tip and you are moving against them (Robbins 2012). Look for a difference: a strand that catches or drags toward the ends in a way it does not near the root. Bleaching raises the friction of hair (Robbins 2012).

Step 3: The wet stretch, a hair elasticity test (the core)

The wet stretch is an elasticity test, not a porosity test: a rough check on the cortex, where damage goes once it gets past the surface. Use one wet hair that has already shed, never one still on your head, because stretching wet hair by about 30% can crack its cuticle even when it is healthy (Robbins 2012). Stretch it gently between your fingers. Healthy hair stretches and springs back. Hair that keeps stretching and stays long, feels gummy, or snaps at once has probably lost structure inside. Damage of this kind shows most when hair is wet, which is why bleached hair can feel fine dry and fragile wet.

Reading your results together

• Roots and ends both bead, both feel smooth, and a wet hair springs back. Low porosity, and very likely healthy hair. It needs less, and no repair treatment, including ours.
• Roots bead; ends spread, soak in or drag. The porosity at your ends is acquired. Measure how far from your scalp the change begins: hair grows about half an inch (a little over a centimeter) a month (Robbins 2012), so a change that starts four inches down dates back roughly eight months. That point may line up with something you remember: a lightening service, a summer, the length you flat-iron. If it does, the damage has a date on it.
• Roots and ends both soak in. If your hair has been colored down to the root, the damage may reach the root. If it has never been colored or lightened, the likeliest reasons are the shape of the fiber, which changes how hair wets and dries, and everyday wear.
• A wet hair over-stretches, feels gummy or snaps. The damage has probably reached the cortex, whatever the spray test says.

Your tests suggest which layers have changed. They can't score how severe the damage is or tell you what to fix first, and the surface can mislead: recently lightened hair can still bead. If anything above pointed to damage, or you couldn't tell, the ANATOMY hair porosity quiz takes your history further. You answer a few questions about color, lightening, heat, washing and how your hair behaves. It scores your porosity (low, balanced or high) and how severe any damage is, then gives you a Damage Profile with a routine matched to it. It is free, takes about a minute, and asks for your email before it shows your profile.

Take the free hair porosity quiz

High vs low porosity hair: the differences

The difference between high and low porosity hair shows first at its surface. Low porosity hair has a sealed surface that sheds water, and it is usually intact. High porosity hair has a stripped or lifted surface that lets water and products in and out easily, and in colored, bleached or heat-styled hair it is usually a sign of damage.

What are the signs of high porosity hair?

The clearest sign is on clean, dry hair: water spreads and soaks in instead of beading. Others:

• The ends feel rougher than the hair near your scalp, and tangle more.
• It feels smooth after conditioner and rough again soon after washing.
• Color and chemical services take faster (Robbins 2012).

What are the signs of low porosity hair?

• Water beads and sits on clean, dry hair.
• The ends feel the same as the hair near your scalp.
• It needs little conditioner, because intact hair binds less of it.

What is medium porosity hair?

Medium porosity hair is the in-between: a mostly intact surface with some wear toward the ends. On the spray test it falls between beading and soaking in, and the ends feel slightly rougher than the roots. It describes plenty of hair that has seen ordinary washing, brushing and sun but no bleach, and it needs maintenance and protection.

Is frizzy hair high or low porosity?

Frizz alone can't tell you your porosity. It has several causes, including humidity, curl, static and surface damage, and damaged, more porous hair usually frizzes more. Under the microscope in one lab study, water on bleached hair spread as thin films that bridged neighboring strands, and as the films dried they pulled the strands out of line (Liu 2022). Curly hair that has never been treated frizzes too, so frizz on its own diagnoses nothing.

Where porosity comes from: born with it, or built up?

In colored, bleached or heat-styled hair, high porosity is usually built up rather than inborn. Bleach, color, hot tools and sun strip the surface and break bonds in the core, and because hair cannot repair itself, the damage accumulates toward the ends (Robbins 2012). Untreated hair can test porous too, usually because of the fiber's shape and everyday wear.

What lightening and color do

Lightening and damage are one reaction. Bleach reacts with the pigment melanin faster than with protein, but it cannot avoid the protein (Robbins 2012; Grosvenor 2018). It also acts fast: in one lab study, a single minute in alkaline hydrogen peroxide nearly tripled the internal surface area of hair; by ten minutes the surface area had fallen back while the damage kept growing, which the authors explained as small pores merging into fewer, larger ones (Hessefort 2008). Bleach works from the outside in, and each layer it reaches is one of the tests above:

1. The surface. Bleach attacks the bonds that anchor 18-MEA. In one study, about 80% of it was gone from the outer surface after a single bleach treatment (Habe 2011). This is the layer the spray test reads.
2. The scales. The material that glues cuticle cells together weakens, so scales lift and chip more easily afterward. The slide test feels this.
3. The cortex. Normal bleaching breaks roughly 15 to 25% of the disulfide bonds, and severe lightening up to about 45% (Robbins 2012). The wet stretch is a rough check for this, and past a certain point hair turns gummy when wet.

Permanent color uses hydrogen peroxide too, at a similarly high pH (Robbins 2012). And damage compounds: in one X-ray imaging study, after the same straightening and flat-iron treatment, hair that had been bleached once showed about three times the porosity of unbleached hair (Lima 2023). The research in more detail: how bleach damages hair.

What heat and sun do

There is no single temperature where heat damage begins. Hot irons have been shown to break down an amino acid in hair (tryptophan) and yellow white hair (Robbins 2012), and damage accelerates above about 200 °C (392 °F), where many flat irons run and where the keratin inside the fiber begins to lose its structure (Zhou 2011; Cao & Leroy 2005). In one lab study, voids inside the cortex multiplied as the iron went from 190 to 220 °C (374 to 428 °F) (Gamez-Garcia 2011). Water makes it worse. In a separate study, the crystalline keratin in dry hair melted at about 205 °C (401 °F), but at about 155 °C (311 °F) when the hair held 23% moisture (Cao & Leroy 2005). Sun strips the surface too. In one study, the equivalent of three summer months of UV removed more than 90% of the surface 18-MEA (Habe 2011).

Who usually has low porosity hair?

Low porosity is not a trait of any group of people. It describes hair, or the part of it, that is new, short, or rarely colored, lightened, heat-styled or sun-exposed. The hair nearest almost anyone's scalp qualifies, unless the roots are colored.

The rest of the strand carries a record. A shoulder-length strand holds two years or more of your life: every lightening, every summer, every pass of the iron, in the order they happened. The section at your scalp is weeks old. The ends were there for all of it. Even hair that has never been chemically treated shows it: in one study, more than 80% of the surface 18-MEA was gone 16 inches (40 cm) from the root (Okamoto 2011).

Which is healthier: high or low porosity hair?

Low porosity hair is usually the healthier state, because it describes an intact fiber. The worst porosity is very high porosity from chemical damage: the surface is stripped, the scales are lifting and bonds in the cortex are broken, so the hair is weakest when it is wet. Untreated hair that tests porous is a different case; the likelier causes are fiber shape and everyday wear.

Low porosity hair needs less, not more

Low porosity hair is usually healthy hair. If your roots and ends both bead and feel smooth, and your hair has not been lightened recently, it does not need reconstruction, bond repair or a treatment mask, including ours. Intact hair binds less conditioner than damaged hair (Robbins 2012), so a gentle shampoo, a light conditioner on the lengths and a clarifying wash now and then, if products build up, are enough.

What it does need is protection: hot tools only on dry hair and at moderate heat, shade from strong sun, and time between color services. More: how to care for low porosity hair.

What not to put on low porosity hair

No ingredient is known to harm low porosity hair as such. What it does not need is repair: reconstruction treatments, heavy protein masks, stacked layers of butters and oils. Warm water speeds water uptake in all hair (Robbins 2012), but we found no evidence that low porosity hair needs heat caps or steam to "open" it.

How to treat high porosity hair

Treat high porosity hair in the order the damage happened. First stop adding to it: space out color, dry hair fully before hot tools and shield it from strong sun. Then treat the surface with conditioner at every wash, and the core with treatments small enough to get inside the fiber. No treatment makes damaged hair new. Good treatment makes it behave more like healthy hair for as long as it stays in or on the fiber: water beads instead of soaking in, the ends slide instead of catching, and the hair partly regains its strength. The full routine: how to treat high porosity hair.

First, stop adding to it

• Space out lightening and color. Each service meets weaker hair than the last.
• Dry hair fully before any hot tool, and turn the iron down.
• Keep it out of strong sun, or cover it.

Then treat the surface

Most conditioning ingredients carry a positive charge, and hair carries a negative one that grows stronger with damage, so conditioners bind most strongly where hair is most damaged: bleached hair took up about ten times more of one conditioning polymer than untreated hair (Robbins 2012). They lower friction and restore some water repellency (Robbins 2012; Liu 2022). They also partly wash out, so surface care belongs in every wash. In one study, a shampoo-strength surfactant removed half of a conditioning polymer within a minute and nearly 70% within half an hour, though some stayed firmly bound (Robbins 2012).

Then treat the core

If a wet hair over-stretched or snapped in your test, this is the layer that failed. Conditioners work mainly at the surface; they do little for the broken bonds in the cortex. Smaller molecules can get further. Damaged hair is more penetrable than intact hair (Robbins 2012), and in one industry-funded study, small keratin peptides reached deep into the cortex of chemically relaxed hair (Malinauskyte 2021). More on what hair bonds are, and what repairing them means.

ANATOMY's two molecules, covered by three granted patents, are built on click chemistry, the reaction class recognized by the 2022 Nobel Prize in Chemistry. The system is Swiss-developed and was independently tested on bleached hair at SGS proderm in Germany. Independent, peer-reviewed evidence for bond-building treatments as a class is still thin, and none of the studies cited here tested ANATOMY. The Complete Reconstruction System works in three steps, and the Leave-In is the step that stays on the hair longest.

Which oil for high porosity hair?

Coconut oil is the best-documented penetrating oil: it gets into the hair shaft where mineral oil does not (Ruetsch 2001), and it was the only one of three oils tested that markedly reduced protein loss from both damaged and undamaged hair (Rele & Mohile 2003). Both studies involved a hair-oil manufacturer.

What to avoid with high porosity hair

• Heat on damp hair. Water lowers the temperature at which hair's crystalline keratin melts (Cao & Leroy 2005).
• Back-to-back chemical services, because damage compounds (Lima 2023).
• Rough detangling while wet, when damaged hair is at its weakest.
• Wetting and drying it more often than you need to. Repeated swelling and drying is named in the research literature as one cause of hair damage, called hygral fatigue (Ruetsch 2001).

Can you change your hair's porosity?

You can raise your hair's porosity easily, but lower it only partly, and only while a treatment is present. Hair cannot repair itself, so its porosity never falls back on its own, and treatments do not regrow cuticle. The one true reset is new growth, or a trim. When someone says their porosity "went back to normal," new growth, a trim or product left on the hair is the likeliest explanation.

What to do with what you found

Low porosity from roots to ends. Do less: a light conditioner, a clarifying wash now and then, and protection from heat and sun. Repeat the spray test every few months, and a few weeks after any color service. The surface is the first layer to go, so your ends are likely to show it first.

Your ends test high and your roots don't, or a wet hair failed the stretch. That is acquired damage, and it has an order: stop adding to it, then treat the surface, then the core. How much each step matters depends on how far the damage has gone, and the quiz scores that from your history. Find your Damage Profile.

Never colored, porous from root to tip. Your hair needs moisture and gentle handling, not reconstruction.

Not sure what you are seeing. Home tests are comparisons, and some heads don't give a clean answer. The quiz comes at the question from the other side: rather than reading your hair, it mostly asks what has been done to it. Take the hair porosity quiz.

Frequently asked questions

If hair floats in water, is it healthy?

Not necessarily. The float test mostly measures surface tension. Hair is denser than water, so every strand sinks eventually; how long it floats depends on surface oils, product residue, how you drop it and how long you wait. A floating strand may simply be coated. Comparing how water beads on your roots and your ends is more informative.

Is bleached hair always high porosity?

Bleached lengths are almost always high porosity, with one catch. Freshly bleached hair can keep some water repellency until washing and wear finish stripping the surface (Tokunaga 2019), so it may bead at first while the damage inside is already done. More: is bleached hair high or low porosity?

What is the worst hair porosity?

Very high porosity from chemical damage. The water-repellent surface is stripped, the scales are lifting and bonds in the cortex are broken, so the hair is weakest exactly when it is wet. Untreated hair that tests porous is a different case: the likelier causes are fiber shape and everyday wear.

Can low porosity hair become high porosity?

Yes. Lightening, permanent color, hot tools on damp hair, sun and years of ordinary wear all raise porosity, and none of it reverses on its own. New growth starts out low porosity; how long it stays that way depends on how you treat it.

Does race or ethnicity determine hair porosity?

No study we could find measures porosity across ancestry groups, so there is no basis for ranking them. A 2023 review found no good evidence that hair from different backgrounds differs in its basic chemistry; the differences lie mainly in shape and curl (Daniels 2023). Tightly curled hair takes more wear from combing (Robbins 2012), but what has been done to hair matters more.

Does hard water affect porous hair?

Damaged hair takes up more of the calcium and magnesium in tap water, and in one lab study those metals stiffened both untreated and bleached hair (Evans 2011). Whether hard water weakens hair is less clear: two small studies disagree (Srinivasan 2013; Luqman 2018). More: hard water and hair.

Porosity is one hair question you can answer tonight, with a spray bottle and your own roots as the evidence. To check your reading against your hair's history, the hair porosity quiz takes about a minute.

References

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3. Okamoto M, Tanji N, Habe T, Inoue S, Tokunaga S, Tanamachi H. ToF-SIMS characterization of the lipid layer on the hair surface. II: effect of the 18-MEA lipid layer on surface hydrophobicity. Surf Interface Anal. 2011;43(1-2):298-301. doi:10.1002/sia.3406. (Kao)
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8. Lima CRRC, et al. Alterations promoted by acid straightening and/or bleaching in hair microstructures. J Appl Crystallogr. 2023;56(4):1002-1014. doi:10.1107/S1600576723005599.
9. Zhou Y, Rigoletto R, Koelmel D, et al. The effect of various cosmetic pretreatments on protecting hair from thermal damage by hot flat ironing. J Cosmet Sci. 2011;62(2):265-282. PMID 21635854. (ISP)
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11. Gamez-Garcia M. Void and pore formation inside the hair cortex by a denaturation and super-contraction process occurring during hair setting with hot irons. J Cosmet Sci. 2011;62(2):109-120. PMID 21635840. (BASF)
12. Malinauskyte E, Shrestha R, Cornwell PA, Gourion-Arsiquaud S, Hindley M. Penetration of different molecular weight hydrolysed keratins into hair fibres and their effects on the physical properties of textured hair. Int J Cosmet Sci. 2021;43(1):26-37. doi:10.1111/ics.12663. (TRI Princeton; Croda funding)
13. Ruetsch SB, Kamath YK, Rele AS, Mohile RB. Secondary ion mass spectrometric investigation of penetration of coconut and mineral oils into human hair fibers: relevance to hair damage. J Cosmet Sci. 2001;52(3):169-184. PMID 11413497. (TRI Princeton; Marico co-authors)
14. Rele AS, Mohile RB. Effect of mineral oil, sunflower oil, and coconut oil on prevention of hair damage. J Cosmet Sci. 2003;54(2):175-192. PMID 12715094. (Marico)
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18. Luqman MW, Ramzan MH, Javaid U, Ali R, Shoaib M, Luqman MA. To evaluate and compare changes in baseline strength of hairs after treating them with deionized water and hard water and its role in hair breakage. Int J Trichology. 2018;10(3):113-117. doi:10.4103/ijt.ijt_115_16.
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20. The Nobel Prize in Chemistry 2022: Carolyn R. Bertozzi, Morten Meldal and K. Barry Sharpless, "for the development of click chemistry and bioorthogonal chemistry." nobelprize.org

About this article

Written by Nawaf Arhamah, founder of ANATOMY, and checked against the sources above. Where a finding comes from a single study, the text says so, and the reference list notes which studies were run or funded by companies. The home tests described here are comparisons, not validated measurements of porosity, and we present them that way. Last updated 22 September 2026.