1. Because the words “female” and “woman” mean different things.
“Female” is a scientific term that refers to the sex of a species that is capable of producing children. The term “woman” refers specifically to human beings, while “female” could refer to any species.
2. Because reducing a woman to her reproductive abilities is dehumanizing and exclusionary.
When you refer to a woman as a female, you’re ignoring the fact that she is a female human. It reduces a woman to her reproductive parts and abilities.
Also, not all women are biologically female, and the conflation of “female” to “woman” erases gender-nonconforming people and members of the trans community.
4. Because it is most often used to imply inferiority or contempt.
Not always, but often. And it’s typically when “female” is used as a noun (i.e., “Females are the worst!”). Here’s a fun exercise: Search the word “females” on Twitter and see what you get.
5. Because it’s grammatically weird.
The word “female,” in its primary usage, is an adjective. When you use “female” as a noun, the subject that you’re referring to is erased.
“I talked to a female yesterday.”
A female what? A female kangaroo? A female rock snake? The subject of the sentence is not clear.
“I talked to a female presidential candidate yesterday.”
This sentence is now about a human being.
It should be noted, though, that using “female” as an adjective can take a sexist turn when used in a case that isn’t notable. Referencing a “female firefighter,” for example, is appropriate only when her being female is pertinent to the story; otherwise, she’s just a firefighter. But if you’re talking about the first woman to become a firefighter, saying “the first female firefighter” is acceptable because her gender is relevant.
For more information on the appropriate grammatical uses of “female” and “woman,” click here.