Some of the causes are illness, side effects from medications, hormonal imbalances of testosterone or estrogen, mental or physical disabilities, depression and alcohol or drug abuse, says Goodwin, author of "A Woman's Guide to Overcoming Sexual Fear and Pain."
Others include sexual trauma such as abuse or rape, negative religious or family training about sex, and problems with body image, Goodwin says.
Sex is psychological for women, while for men it's very physical, Mandel says.
After childbirth, a woman often experiences a decreased sex drive.
The demands on her time and energy become much greater, and intimacy often gets rationed out, Solberg says.
"Even if they close the door to the bedroom, most mothers will have one ear open to see if their child needs something," Solberg says.
Solberg says decreased sex drive also occurs in those who are very career-oriented and devote a lot of mental and physical energy to their jobs.
Others may lose interest if they experience physical pain during sex, or if they are having problems communicating with their partner.
What you can do
Recognizing there is a problem is the first step, Mandel says.
"There are real reasons why it happens, and it's OK to seek care. There's nothing creepy or crazy about it," Mandel says.
The worst thing you can do is to be unhappy with the way you feel but do nothing about it, Solberg says.
"For the majority of women, it's a matter of needing a kick start to get the process going," Solberg says.
If diminished sex drive is being caused by a medical condition, a change in medication may help, Solberg says.
When stress is a factor, allow yourself time to relax by taking a bath or a long walk.
Exercise improves libido by increasing overall health, Mandel says.
"Anything that makes you feel poorly will impact your interest in sex," Mandel says.
When the problem is interfering with your relationship, it's time to do something about it, Goodwin says.
If you don't feel comfortable talking to your partner about the subject, make a list of conditions that need to be met in order for you to enjoy sex. They may include privacy, freedom from interruption or pain, or not being tired, stressed out or angry, Goodwin says. Share the list with your partner.
While diminished sex drive is a difficult subject to discuss with your doctor, it's an even tougher topic to talk about with your partner, because often he will feel rejected, Mandel says.
"You have to be careful to make your spouse understand it's not something he's done or not done," Mandel says.
When Oprah Winfrey featured the topic on her talk show a few months ago, Mandel and Solberg both got many calls from patients.
On the show, actress Cristina Ferrare said she solved her problem of low sex drive by using testosterone cream.
Testosterone creams have not been proven, and they tend to increase cholesterol levels and can promote the growth of facial hair, Solberg says.
Medications aren't without their risks, and people can't just take testosterone and not be vigilant, Mandel says.
Solberg says many women want reassurance that they are normal.
"Whatever is satisfying to both members of the couple is normal," he says.
What are the causes?