Why are women often carriers of X linked traits but rarely affected by them?

X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. Women have two X chromosomes; men have one X and one Y. Genes on the X chromosome can be recessive or dominant. Their expression in females and males is not the same.

Women have 2 X chromosomes, unlike men who have XY. In women, a recessive allele on one X chromosome is often masked in their phenotype by a dominant normal allele on the other.

Explanation:

In informal words, if you have an X-linked trait that is recessive and are male, you will be affected cuz there is no other X to "override" that recessive trait because Y is (as we know) non-coding. Whereas if you are female, both of your Xs would have to carry a recessive trait for you to be affected, thus it is rarer for women to be affected by X-linked traits.