Actually, women can and some have, caused nerve damage to their clitoris because of the way they force multiple orgasms by using vibrators repeatedly on the specific area. The area becomes numb and it doesn't seem to stimulate like it used to, this can last days to weeks or even permanently depending on how 'hard' she was pressing to try and bring about another climax. It's recommended that she stop using the vibrator and allow herself time to rest from masturbation completely until her body gives her natural signals of arousal; and even then, go for a more natural method of release. Waiting and allowing your body (male or female) to build up in arousal can lead to a more satisfying climax and release in the end.
But as people have said, everything in moderation. Masturbation (in moderation) can and is a good thing for men and women to practice, either with themselves or with a partner - commonly known as 'mutual masturbation'. Masturbation is good for the following reasons: Reduces stress, it's a release of sexual tension, is thought to have a positive effect on your immune system, body image, and psychological health; and for men ejaculation helps reduce the risks of prostate cancers.
Masturbating once or twice every few days is usually the norm for most people (though that tends to vary on living situation and relationship status), and allows them time for other things in life instead of the constant pursuit of...well, touching themselves all the time. However, the younger you are (tween/teen years) the more frequently you tend to masturbate and focus more on your sexual urges, since they are just beginning to come about in a big way and you find most of your masturbating sessions are self-discovery on what arouses you and what feels the best.
