If you don’t talk to your teen about sex ...

DEAR DOCTOR K >> I’m the parent of a teenage girl. I know it’s time to talk to her about sex, and I’d appreciate any advice. DEAR READER >> Many parents feel anxious or uncomfortable talking with their children about sex. But remember that if you don’t, somebody else will.

Teens get lots of information (and misinformation) about sex from their friends, the internet, television, magazines, books and movies. It’s up to you to make your child understand what it really means to have sex, both physically and emotionally.

Don’t worry that you will be “putting ideas” into your teen’s head. Many parents I’ve talked to are concerned that having the conversation will encourage their kids to try it. In fact, teens who talk openly with their parents usually wait longer to have sex — and they are more likely to use birth control when they do.

Whether to have sex outside of marriage is a personal question, and I’m not going to weigh in on that. But it is important that you state your own views regarding at what point in a relationship sex is appropriate. At the same time, don’t insist that your child share your views. My colleagues who specialize in adolescent medicine tell me that teens often are naturally rebellious and resist attempts to tell them what to do.

It is very important to teach your child how to say no firmly. Coach your daughter to say “no” while looking her partner in the face. Again, it’s one thing to talk to your daughter about how to say “no,” and it’s another to tell her when.

I wouldn’t describe all of the sexually transmitted infections (STIs) in detail. That can come across as scare-mongering and cause some kids to tune out. But I would list all of the STIs: Most kids don’t realize how many there are.

By the same token, I wouldn’t stress that some of them, if unrecognized and untreated, can be fatal. I would emphasize that some of them can make it hard or impossible for a woman to bear children.

I would describe the facts about birth control. The points I’d be sure to make are that no birth control is 100 percent effective, and that many types of birth control will not protect against STIs. The only way to be entirely safe is not to have sex.

Finally, I’d explain that sexually active females need to have a pelvic exam every year. Offer to take her to a gynecologist or pediatrician if and when she decides to have sex.

Most important, be there for your teenager. Listen to her questions and try to answer every one. Let her know that whatever choices she makes, she will always have your love and support.

(This column ran originally in October 2013.)