Which factor can contribute to ingrown hairs?

Using both a dull razor and shaving against hair growth can contribute to the formation of ingrown hairs. A dull razor does not provide a clean cut as effectively as a sharp one, leading to hair that is more likely to bend or curl back into the skin as it grows out. This can create irritation and the potential for ingrown hairs.

Shaving against the direction of hair growth can also exacerbate this issue. When the razor cuts the hair at an angle or too close to the skin, it can create sharp edges on the hair, which increases the likelihood of the hair growing back into the skin rather than outward. This combination of using improper shaving techniques and tools clearly indicates that both factors are significant contributors to the problem of ingrown hairs.