I often catch my younger sister touching her self.
I don't know of any scripture to tell her to stop.
She says there's no harm because she's not having sex with anybody.
Do you know of any thing in the Bible I can point out?

GOOD MORALS REPLIES::

She is having sex with herself, which is wrong because it is a form of homosexual behavior: sex with a person of the same sex. It is also wrong to stir up the lusts of the flesh outside the marriage covenant. Single people have an obligation to keep the flesh under, not indulge it.

The following links should be helpful.

http://goodmorals.org/Ratzinger.htm
http://www.rtforum.org/lt/lt67.html
http://goodmorals.org/sterile.html

Purity applies to actions with yourself as well as with other people.

Abstain from all appearance of evil. I Thessalonians 5:22

Dearly beloved, I beseech you as strangers and pilgrims, abstain from fleshly lusts, which war against the soul. I Peter 2:11