Does Hair Porosity Affect Hair Colour? What Is Measured and What Isn't

Possibly, but its effect on permanent colour has not been measured: in lab tests, bleached or melanin-free fibres showed a bigger colour change from a natural dye, and permed hair took up about twice as much of a drug, as normal hair. Nobody has measured permanent colour going darker or ashier on porous ends, or ends on a real head being more porous than roots, so treat the ends as the least predictable part of any head and strand test them rather than assume.

Does hair porosity affect hair colour?

Damage changes the fibre, and that may change how colour behaves, but no study links the change to permanent colour, and the change is not simple. In a gas-sorption study, bleach nearly tripled hair's surface area within a minute, then that area fell after 10 minutes. "More damage, more porous" does not hold at every stage.

In the salon, porosity means how readily hair takes up product. In the lab it means several different readings (gas-reachable surface area, fibre density, water contact angle, water uptake), and no study checks them against each other or against what a colourist feels in the hand.

Gas sorption measures the surface a gas can reach inside cut fibres, a stand-in for pores. The authors put the first-minute rise down to new pores forming and the sudden drop after 10 minutes to small pores merging into larger ones. The study does not give the bleach formulation, so how those time points map onto a salon lightening service is not known. UV did the opposite at first: surface area fell over the first 200 hours of exposure, then crept up.

The surface changes too. On fibres from one never-treated donor, the advancing water contact angle measured on the fibres was around 90°. After four alkaline colourings combined with lab weathering the authors say simulated a year, it was around 65°, meaning the surface had become more water-loving. Most of the 18-MEA, the thin fatty layer that makes healthy cuticle shed water, was gone. The authors put the change down to that loss and to oxidation of surface sulfur (the second part not measured). Colour and weathering were applied together, so the colour's share can't be separated out. A 2015 review for dermatologists describes damaged hair as "intensely" porous and says water swells the shaft.

What to do with that: "porosity" on a consultation card is a judgement, not a measurement. Record what you see and feel, and what has been done to the hair — lightening, perms, heat, how many colour services the ends have had. Reading the hair, not the photo covers that consultation read.

Why does colour grab on porous ends?

Porous ends may well take colour faster, but that has only been shown with a natural dye and a drug, not permanent colour. Bleached or melanin-free fibres showed a bigger colour change from a natural dye, and permed hair took up more of a drug, than normal hair. Colourists treat porous ends as quick to grab. That is a sound working rule, and the reason to strand test, but no study has measured it for permanent colour.

Another possibility, also untested, is colour building up over repeated, overlapping applications down the lengths, and no study compares the two. Refreshing mid-lengths and ends is built around this one: keep fresh colour off lengths that already hold it.

The closest evidence is a 2020 Vienna study co-written by a cosmetics maker, using logwood, a natural dye. Natural human hair gave a "rather constant" colour change whatever its starting shade. Bleached extension hair and melanin-free yak hair both showed a "much stronger" change. Yak hair was more porous at every scale measured; its density was about 1.07 g/cm³ against 1.31 for human hair. The authors credit porosity first, then fewer scales and no melanin, without separating them. They did not measure the bleached hair's porosity at all.

The study measured colour change, not the amount of dye in the hair. A lighter starting fibre may also show a bigger visible change for the same amount of dye, because there is no darker base to hide it, so part of that "much stronger" result may be the pale starting colour, not extra uptake. Logwood is not an oxidative colour either.

In a forensic hair-testing patent, permed hair soaked in a drug solution took up about twice as much as unpermed hair (an average of 52 against 26 ng per 10 mg of hair, five samples each, overlapping ranges, hair of unknown history). It is a drug, not a dye.

What to do: ends that are lightened, permed or long-processed are where a shade is least predictable. Strand test the ends with the formula you plan to use, and keep fresh permanent colour off lengths that don't need it.

Does porous hair hold colour?

Not shown either way. One lab study found that bleached and natural white swatches changed colour much more than brown ones after permanent auburn shades were faded. Its published summary gives no numbers for that comparison, offers no mechanism and does not mention porosity.

That 2005 study coloured swatches with commercial two-part permanent dyes in auburn shades, then faded them with a weatherometer, repeated shampooing, or both. Coloured white hair and coloured bleached hair underwent "much greater change" than coloured brown hair. It covers auburn shades only; there is no comparable data for ash, blonde or dark shades. The same caveat applies: with no darker base to mask the same loss, a bigger visible change is not proof that more dye left the hair.

What to do: tell lightened and white-haired clients that their colour change may show sooner, possibly because there is less natural depth underneath to mask it. Manage the things that are measured to fade colour, washing and light, rather than promising a porosity fix.

What isn't known yet: grey hair, the float test and fillers

What porosity is grey hair? In untreated salt-and-pepper hair, a 2011 study found few differences across people between grey and pigmented fibres in water uptake, surface energy and stiffness. Within many individuals the fibres did differ, more in bulk than at the surface; the authors call the differences "small" but say they lend some support to grey hair feeling drier. A 2018 study of how grey hair moves refers to grey fibres being thicker, but reports that as background, not as a measurement. Neither study reports porosity or how well grey takes colour, so nothing establishes grey hair as low porosity. Colourists do meet white that resists colour, and the grey coverage formula is built for it. One point is supported: a review for dermatologists says permanent colour covers grey better than demi-permanent, which places dye closer to the surface (why demi sits shallower).

Does the hair porosity float test work? No study tests it. One study measured dry single fibres as denser than water (human 1.31 g/cm³, more porous yak 1.07 g/cm³), but it did not test flotation, and dry density alone does not tell you whether a wet strand floats. A patent application says a floating strand is porous and heat-damaged, with no data behind it. Use the feel of the hair and its history instead.

What's the worst hair porosity to have? There is no validated low, medium and high porosity scale in the published research. A 2023 review of how hair types are classified does not use porosity as an axis, and no study ranks porosity grades or matches a dye type to them.

Fillers and developer on the ends. No peer-reviewed study tests protein or pigment fillers, pre-pigmentation or porosity equalisers on porous hair. A review notes that bleached hair carries more negative charge and so attracts conditioning ingredients, but it says nothing about pre-treating before colour, and no study tests whether that evens out colour uptake. For developer strength, timing and reflect choice on porous ends, work to the manufacturer's instructions. UK law caps hair products at 12% hydrogen peroxide (40 vol); that is a legal ceiling, not advice on what to use on ends. No study covers the breakage risk of porous ends under oxidative colour.

What to do: follow the manufacturer's instructions for any corrective step, and strand test before adding a filler or pre-pigment stage. When a result goes wrong, correcting colour gone wrong covers the fixes.

What this means when you colour with Life Color Plus

Life Color Plus is an ammonia-based oxidative permanent, so porous ends are as unpredictable with it as with any permanent: read the ends, strand test them with your actual formula, and keep fresh colour off lengths that don't need it. No study tests Life Color Plus, or any named permanent, on porous hair.

Read the ends at consultation and write down their history (the consultation guide). Strand test the ends with the formula you intend to use, mixed at the ratio the service calls for: 1:1.5 standard, 1:1 for heavy white or a more intense result, 1:2 for the 900 and 12 superlighteners (see mixing ratios in practice). And keep fresh colour off lengths that don't need it, using the mid-lengths and ends method.

The cream developer runs 10, 20, 30 and 40 vol (3, 6, 9 and 12%). The developer decision guide covers which volume does which job.

Summary: what is measured and what isn't

Related: Refreshing Mid-Lengths and Ends Without Over-Darkening, Going Darker With Life Color Plus and Correcting a Colour That Has Gone Wrong.

Colour chemistry: questions colourists ask.
See also: Underlying pigment explained · Refreshing mid-lengths and ends · Correcting colour gone wrong
Shades: Life Color Plus tubes, £3.49

Sourced to Hessefort, Holland & Cloud (2008), Tanamachi et al. (2009) and Locke & Jachowicz (2005), all in the Journal of Cosmetic Science; Gavazzoni Dias (2015), International Journal of Trichology; Müllner et al. (2020), Molecules; Kaplan et al. (2011), International Journal of Cosmetic Science; Bechthold, Wiesche & Wortmann (2018), Journal of Cosmetic Science; Daniels, Fraser & Westgate (2023), International Journal of Cosmetic Science; UK-retained Regulation (EC) 1223/2009, Annex III; and patent documents EP 3 039 432 B1 (Psychemedics) and WO2025137404A1 (K18). Always work to the instructions supplied with the product you are using.