Hair Porosity
Hair porosity describes how readily the hair shaft absorbs and releases water and chemicals. It is determined primarily by the condition of the cuticle (overlapping scale cells): intact cuticles yield low porosity, while lifted/damaged cuticles yield high porosity.
Categories
- Low porosity: cuticle layers lie flat and resist moisture uptake; products may sit on the surface unless heat or light mechanical action is used.
- Normal/medium porosity: balanced uptake and retention; most hair types fall here.
- High porosity: raised or missing cuticle areas allow rapid uptake and loss of moisture and dye; often a consequence of chemical or thermal damage.
Practical implications
- Dyeing: high porosity hair accepts dye quickly but also loses pigment faster and can appear uneven; use lower developer strengths and fill with protein or colour‑filling products when lightening.
Lightening note: porosity strongly determines how hair responds to bleaching — highly porous hair will lift unevenly and is more susceptible to over‑processing. Strand tests and conservative developer selection (or staged lifts) help preserve integrity. See: Hair Bleaching.
- Hydration: high porosity hair benefits from occlusive conditioners, leave‑ins and periodic protein treatments to rebalance moisture–protein matrix.
- Styling: low porosity hair responds better to heat or steam to help products penetrate; clarifying cleansers may be needed where buildup prevents wetting.
Testing porosity
- The simple water test (a single strand placed in water to observe sinking) is common but imprecise; professional assessment uses laboratory techniques or trained evaluation of wetting behaviour.
Writing tips
- Use porosity as an invisible detail to signal hair history: "the ends drank the oil like dry earth" hints at high porosity from prior processing.