Which factor can negatively impact the moisture retention of hair?

High porosity is a factor that negatively impacts the moisture retention of hair due to its structure. Hair with high porosity has gaps and holes in the cuticle layer, which makes it more absorbent and likely to lose moisture quickly. While high porosity can initially allow moisture to enter the hair shaft, it does not retain moisture effectively because the cuticle is unable to lay flat to hold in the moisture. This can lead to hair that feels dry and brittle, as it cannot maintain the hydration needed for healthy hair.

The other factors listed do not have the same negative impact on moisture retention. For instance, high humidity levels can actually increase moisture retention for hair, while low porosity hair tends to retain moisture better because its cuticle is tightly sealed, reducing moisture loss. Excessive oiliness may contribute to a greasy appearance but does not necessarily equate to poor moisture retention; in fact, it may help to keep hair hydrated depending on the types of oils present.