Which test involves holding a strand of hair with one hand and sliding the thumb and forefinger from end to scalp?

The porosity test is designed to assess how well hair can absorb and retain moisture, which is essential for determining the suitability of hair treatments and products. This test involves taking a strand of hair and sliding your thumb and forefinger from the ends towards the scalp. The ease with which your fingers move along the hair strand provides insight into the hair's condition. If the hair slides easily, it may indicate that the hair is highly porous, meaning it has gaps or holes in the cuticle layer that allow moisture to enter and escape easily. This could suggest that the hair may be damaged or over-processed. In contrast, if there's resistance while sliding the fingers, it suggests lower porosity, indicating that the hair cuticle is closed and the hair is less damaged, which can retain moisture more effectively.

Understanding porosity is crucial for making informed decisions about product use, moisture retention, and overall hair health, especially in a cosmetology context.