The notion that women lose interest in sexual activity after menopause has collapsed under scientific scrutiny. In a survey of 27,000 women enrolled in the Women's Health Initiative (WHI), more than 60% of women in their 50s, 45% of those in their 60s, and 28% of women in their 70s reported that they were sexually active, and almost two-thirds said they were happy with their level of sexual activity. Of those who were dissatisfied, more than half said they would prefer having sex more often. The study was reported in Menopause: The Journal of the North American Menopause Society (November 2011).

Many smaller studies corroborate the WHI results. All in all, it's become clear that older women are more sexually active than is commonly believed. For example, a 2003 survey of 2,000 women conducted at the University of Michigan found that 46% of women in their 50s and 20% of women ages 60 and over were sexually active. A 2009 survey by researchers at the University of California at San Francisco indicated that 60% of 1,977 women ages 45 to 80 were sexually active.

These findings probably come as little surprise to older women themselves. After all, women who are now in their 60s and 70s came of age during the so-called sexual revolution, when sexual stigmas and inhibitions were falling away, especially for women. And menopause has brought additional freedom from worries about pregnancy. Topical estrogen and lubricants for treating vaginal dryness — as well as sildenafil (Viagra) and other medications for erectile dysfunction — have helped couples continue their sex lives longer and improved the opportunities for women who are widowed, divorced, or otherwise single to enter into sexual relationships later in life.

But apparently, many of these women believe they have outgrown the need for safer sex practices. For example, the 2003 study cited above found that few of the women questioned — even those who were in new relationships or had multiple partners — were having protected sex. Only 13% of single women over age 60 reported using condoms. Perhaps it's because in the 1960s and '70s, before the advent of AIDS, most women thought about condoms only in connection with birth control. Low rates of condom use might also reflect women's hesitancy about broaching the topic of safer sexual practices with partners who might be reluctant. And women who've been in long-term monogamous relationships may be unaccustomed to thinking about taking such precautions when their circumstances change. Finally, public health messages about safer sex practices are targeted mainly at younger women.

Unprotected sex: Still risky after all these years

With many older women enjoying sex and few using condoms, it's not surprising that some are acquiring sexually transmitted infections (STIs). According to the Centers for Disease Control and Prevention (CDC), 3,580 women over age 45 were diagnosed with AIDS in 2009 — more than the number of new diagnoses among women ages 35 to 44 (2,796) and nearly twice the number of new cases among women ages 25 to 34 (1,916). (It's important to note that this doesn't necessarily mean that they acquired the infection after age 45.)

There's also been an uptick in other STIs in postmenopausal women. At the July 2011 meeting of the International Society for STI Research, a Johns Hopkins team studying trichomoniasis, or "trich," reported that the highest rate of infection among the 7,593 participating women — 13% — occurred in those over age 50. In comparison, 11% of women in their 40s and 8.3% of women in their 20s had trich.

Condom use may be especially important for postmenopausal women, because they are more vulnerable to STIs than younger women, for several reasons. As estrogen levels drop off after menopause, the vaginal and cervical tissues thin. This condition, called vaginal atrophy, makes the vaginal lining vulnerable to small tears and abrasions, which provide points of entry for viruses and bacteria. In addition, age-related decline in immune response may make it harder to fight off an STI. And STIs in older women may go undetected because they are often without symptoms, and clinicians aren't always tuned in to screening older women.

A refresher course on STIs

STIs are infections that can be passed between women and their partners of either sex through vaginal, oral, or anal sexual activity. These infections pass more readily from men to women than vice versa; they're also less likely to cause early symptoms in women, making them harder to diagnose before they become a serious problem. STIs of concern include the following:

Human papilloma virus (HPV).The most common STI in women is HPV, which causes genital warts and is linked to cervical and anal cancers. Examining nearly 2,000 participants in the National Health and Nutrition Education Survey revealed that 20% of women in their 50s were infected with at least one of the 38 HPV strains; about half of these women were carrying one of the high-risk strains associated with cervical cancer. High-risk HPV is detected by a DNA test performed in conjunction with a Pap smear. The virus can't be eradicated with drugs. In younger women, it usually clears from the body on its own within two years of infection. In older women, newly acquired HPV may not clear so readily, and more surveillance is required. Cervical cancer can be prevented by removing precancerous lesions, which are identified by Pap smear followed by colposcopy (an examination of the cervix with a magnifying device) and biopsy.

Herpes.Twice as many women as men are infected with herpes simplex virus type 2 (HSV-2), which causes most cases of genital herpes and is spread through sexual contact. Herpes simplex virus type 1 (HSV-1), the type associated with cold sores or fever blisters, can also be transmitted to the genital area, through oral sex. Symptoms of genital herpes in women sometimes include small blisters on the labia or rectum that break and eventually heal. Most infected people have few symptoms, especially after the initial outbreak, although HSV-1 and HSV-2 stay in the body indefinitely and may flare occasionally. It's possible to infect a partner — even without symptoms of an active infection. Condoms reduce but do not eliminate the possibility of transmitting HSV. HSV-2 is usually diagnosed by visual inspection and by taking a sample from a blister and testing it in the laboratory. There's no way to get rid of the virus, but antiviral drugs may reduce the number and severity of outbreaks and lower the risk of transmitting the infection.

Trichomoniasis.The most common symptoms of this condition, which results from infection by the protozoan Trichomonas vaginalis, are vaginal itching and a yellow-green discharge. It's usually diagnosed during a pelvic exam and can be eradicated with a single oral dose of either metronidazole (Flagyl) or tinidazole (Tindamax). However, you can easily get it again through sex with an infected partner, so, as with all treatable STIs, your partner must also be treated to avoid this.

Chlamydia.Chlamydia, which is caused by the bacterium Chlamydia trachomatis, affects fewer than one in 2,000 persons (of either sex) over age 50, but it can cause chronic pain and pelvic inflammatory disease if it spreads from the vagina into the fallopian tubes and uterus. Symptoms in women are usually mild — primarily vaginal discharge, burning during urination, or both — while symptoms in men (usually a penile discharge) are more severe. Chlamydia can be diagnosed by a urine or cervical test and eradicated with antibiotics like azithromycin (Zithromax) or doxycycline (Vibramycin).

Gonorrhea.This disease, which is caused by a bacterium, can affect the entire reproductive tract as well as the anus, mouth, throat, and eyes. It is rare in older people, affecting about one in 2,000 men and one in 10,000 women over age 50. The symptoms resemble those of chlamydia and can include pelvic inflammatory disease. Gonorrhea can be cured with antibiotics if it is caught early, but antibiotic treatment will not always reverse pelvic inflammatory disease, arthritis, and other complications of advanced gonorrhea.

HIV/AIDS.Women are far more likely than men to acquire HIV through heterosexual activity. The rate of HIV infection is holding steady over all for people over age 45, but there is some evidence that it's increasing in older women. In the early stages, AIDS symptoms like fatigue, aches and pains, and short-term memory loss may be overlooked because they resemble common complaints of aging. HIV infection is diagnosed with a blood test and treated with a drug regimen called highly active antiretroviral therapy (HAART). Although HAART has transformed HIV infection from a near guarantee to develop AIDS into a chronic condition, both the infection and the treatment may exacerbate bone loss and unfavorable cholesterol levels.

Hepatitis B and C.The hepatitis B virus (HBV) and, to a lesser extent, the hepatitis C virus (HCV) can be sexually transmitted. Both forms of hepatitis begin with flulike symptoms that eventually go away, and both can be detected by blood tests. If the virus isn't eliminated from the body, it can initiate a chronic liver infection that, over decades, may result in cirrhosis or liver cancer.

Syphilis.Syphilis is rare in women over age 45. According to the CDC's most recent surveillance data, 217 cases were reported in this age group in 2010 — down from 267 cases in 2009. The first sign of the disease is a small, round, painless nodule (chancre) at the spot where the syphilis bacterium entered the body. The chancre heals within a few weeks on its own, but unless it's treated at this early state with an injection of penicillin, the disease will advance to a second stage, with a rash and flulike symptoms. Untreated syphilis can progress to a late stage in which it can damage the brain, nerves, bones, heart, joints, and blood vessels.

Safer sex for any age

If you're starting a new relationship with a potential sexual partner, the following suggestions, which you may have heard back in your teens or 20s, are still applicable today:

Have a talk. It may feel awkward to bring up the subject of sex and safer sexual practices early in a new relationship, but it's important to discuss the issue well before you're about to have sex (a time when you might make a hasty or risky decision). Let your partner know about any infections you may have had, and expect him or her to respond in kind. Discuss the use of condoms or latex dams (for oral sex). You may also want to think about how you might negotiate if your partner is resistant to having safer sex.

See your clinician.Before you start a new sexual relationship, have your gynecologist or internist perform a thorough exam. If you're worried about any STI at all, ask to be tested, and ask your partner to do the same. Get treatment for any bacterial infections, and find out whether you have any viral infections (such as herpes) that warrant the use of condoms or latex dams.

Make some plans. If you are both free of STIs, decide whether you intend to be monogamous and can enjoy unprotected sex at little risk, or prefer to use condoms or latex dams.

Be prepared.If there's any chance you might have sex with someone you've just met, carry condoms with you. Don't have sex if your partner refuses to use a condom.