Good answer

Actually, the Bible doesn't say a single thing about masturbation, and therefore it is not identified as a sin. Gen. 38.9 is a passage and story that includes coitus interruptus (spilling his sperm on the ground and wasting it), but that's not the same thing. In that particular story, it was an offense to the widow. Nothing is said to give an idea that wasting his sperm on the ground was wrong because it would equate to killing. Besides, the ancients didn't know biology to the extent that we do and wouldn't have thought anything was being killed.

So the Bible doesn't say anything about masturbation being wrong. Christian opinions about masturbation span the whole gamut, since the Bible doesn't teach on it. Pastor Charlie Shedd (he and his wife wrote books about sex) says, "Masturbation is a gift of God." Dr. Jay Adams, Christian psychologist says exactly the opposite: "Masturbation is clearly wrong since it constitutes a perversion of the sexual act." Lewis Smedes takes more of a middle road: "The mood today is that masturbation is all right; only the guilt is bad. I do not want to dispute the modern attitude. ... The young person...needs to learn that the feeling of emptiness after masturbating is not guilt, but only incompleteness. In this way masturbation can be accepted, along with its frustrations, as a temporary plateau for his sexuality. It is not morally wrong, but neither is it personally sufficient." John White, pastor and teacher, says, "It is better to masturbate than to burn. I am glad that the younger generation has been relieved of a burden of guilt and fear that once haunted so many of us.... Masturbation is not a good thing, but neither is it a heinous sin." Dr. James Dobson weighs in with: "It is my opinion that masturbation is not much of an issue with God. It's a normal part of adolescence which involves no one else. It does not cause disease, it does not produce babies, and Jesus did not mention it in the Bible." Gary Collins and David Seamands claim, "It's high time we stop making such a 'big deal' out of masturbation and give it the well-deserved unimportance it merits."

I hope this helps. Since the Bible doesn't make a single comment about masturbation, your perception of male masturbation is a misunderstanding, and therefore your wondering about female masturbation being an exception is also a misunderstanding.

From what I understand (please correct me if I’m incorrect), the main reason why Christians consider masturbation wrong is because they’re largely pro-life (so to speak) and believe that no version of it should be wasted as it would equate to killing, which, again, is a sin. And while that can apply to male masturbation because there’s sperm involved, female masturbation has no such consequences - no egg is lost. The secretion doesn’t contain potential living organisms. The only consequence is that it feels good. So why is it considered wrong?