Sex isn't always a healthy choice. Impulsive decisions can lead to lifelong problems: serious disease and infertility. The fact that more than three quarters of the sexually active population has at least one sexually transmitted disease (STD) is a sign of the failure of society to educate people to make smart choices. It's especially disheartening since most STDs are preventable through simple behavioral changes—changes that can save your life, preserve your ability to have children, and make the sexual experience more enjoyable, because you won't be worrying about the possible consequences.

Most of the bacterial diseases that can be transmitted sexually are curable. . . if they're found in time. Unfortunately, a majority of STDs are asymptomatic, that is, there are no obvious external symptoms-and people often have no idea they have them until years after they've been infected. Those years of ignorance not only provide an opportunity for them to spread the disease to others, but also for the disease to wreak havoc on their reproductive tracts and some times elsewhere in the body. On a positive note, all of the side effects of bacterial STDs can be prevented by consistent condom use for both penetrative and oral sex, since some of these diseases can also be transmitted through the mouth.

Different sexually transmitted diseases lurk in different parts of the reproductive tract, depending on where they "like” to do their damage. Protozoa loiter in the vagina, infecting anyone they can get their cilia on. Higher up around the cervix is where the bacteria—chlamydia and gonorrhea—go to steal young women's fertility. Finally, there's syphilis, one of the deadliest of the bunch, waiting for its chance to pounce.

Chlamydia and gonorrhea are two of the most commonly diagnosed sexually transmitted diseases. Both are highly asymptomatic—more than 96 percent of individuals with chlamydia and approximately half of individuals with gonorrhea have no symptoms.

Even when they cause no symptoms, chlamydia and gonorrhea increase the risk of acquiring other infections such as HIV. In addition, if left untreated, these infections can lead to infertility and other serious health consequences. Most cases of these diseases occur in people in their teens and twenties, in part because women of younger ages are more susceptible due to differences in their cervix; a young woman has a more delicate cervix than an older woman, making her easier to infect.

What did Christopher Columbus, Abraham and Mary Todd Lincoln, and Vincent Van Gogh Have in Common?

They all probably had syphilis.

Syphilis is a very nasty disease that can do very serious damage to the human body-including the brain—if left untreated. Unlike the other curable STDs, it causes not just a localized infection, but a systemic one. In its first stage, it produces genital ulcers. In its later stages, after the ulcers have healed, it can damage most of the body's systems. Numerous famous people have suffered from syphilis, and some historians have wondered if it played any role in their sometimes erratic behavior. It can, after all, have some pretty strange personality effects.

Trichomonas vaginalis is one of the most common sexually transmitted diseases in the United States. It's caused by a protozoa—a small one-celled organism with a four-stranded tail—and it is relatively easy to identify during a medical exam. Interestingly, it's the only one of the curable STDs for which infection becomes more common with increasing age. Just like chlamydia and gonorrhea, it's associated with increased risk for HIV, as well as multiple health complications, and it can even affect pregnancy.

Two of the most common currently incurable STDs are caused by viruses. They don't, however, have very much in common, other than very similar three-letter acronyms.

A person who has herpes, or the herpes simplex virus (HSV), may actually have one of two different conditions. Oral herpes is usually caused by HSV 1. This is the virus that causes cold sores, although many people have no symptoms. 50 percent to 80 percent of the U.S. population is positive for oral herpes-they normally acquire it as children from kissing their relatives. Genital herpes is usually caused by HSV 2, and it causes similar sores in the genital region. Almost one in four Americans is positive for genital herpes, although it's asymptomatic in 90 percent of cases. It's important for people to know, however, that herpes can still be contagious even when no sores are present and that oral sex can transmit herpes from the mouth to the genitals and vice versa.

Human papilloma virus (HPV) is the virus responsible for both genital warts and several reproductive cancers. Virtually all, if not all, cases of cervical cancer are caused by HPV, as are many cases of anal, rectal, and penile cancer. There are more than 70 types of HPV, but fewer than 30 are transmitted sexually and only a small subset of those are cancer-causing. Unfortunately, even consistent condom use cannot completely prevent the spread of HPV, since it is spread by skin-to-skin contact, and not solely by secretions. This may be why more than 75 percent of the population has been infected with at least one type of HPV. There is hope, however, since vaccines to prevent the most dangerous strains of the virus will soon be available.

Human immunodeficiency virus (HIV) is the virus that causes AIDS. It is not a disease limited to gay men, injection drug users, or the morally weak. It is not a plague sent down by God. It is a terrible virus that is devastating the people of the world. It is also highly preventable. If everyone followed safer sex and universal precautions for infectious disease, there would be no new infections caused by this fragile, difficult-to-transmit virus. Unfortunately, being safe is not always easy. Some individuals are powerless to negotiate condom use, and others recognize it would be dangerous to try. Others don't want to risk their sexual enjoyment by using latex barriers for oral, manual, anal, or vaginal sex. Heterosexual women are the fastest-growing group of infected individuals in much of the world, because many cannot, or will not, ask for safer sex from their male partners. In places and situations where women are valued only for their child-bearing capabilities, a woman who insists on using a condom is viewed as being useless. More than that, she's viewed as not trusting her mate, which can cost her her relationship with the man who may be her sole source of support. It may even cost her her life.

Although infection with HIV is no longer a death sentence, it is still an incredibly serious disease. HIV is dangerous because it weakens the immune system, which makes infected individuals susceptible to many types of diseases that healthy people could easily avoid. Those infections are what kill a person with AIDS, not the virus that has made them so easy to infect. HIV is very difficult to treat. Although the drugs are constantly improving, the treatment regimens are difficult to follow, and many of the drugs have side effects that can feel far worse than the disease. And in many developing countries, the drugs may be too expensive for people to afford.

HIV OR AIDS?

To be diagnosed with AIDS, a person must be HIV-positive and must either have a CD4 (type of immune cell) count below 200 cells/mm3, or one of the AIDS-defining conditions below. It is possible to go from having AIDS back to simply being HIV-positive if a person's immune system rebounds or if he or she recovers from the defining infection.

AIDS-defining conditions:

• Candidiasis-yeast infection
• Cervical cancer (invasive)
• Coccidioidomycosis-a type of fungal infection
• Cryptococcosis-a type of fungal infection
• Cryptosporidiosis-a severe diarrheal disease caused by a water-borne parasite
• Cytomegalovirus disease-a type of viral infection
• HIV-related encephalopathy-alteration of the brain
• Herpes simplex (severe infection)
• Histoplasmosis-a type of fungal infection
• Isosporiasis-a severe diarrheal disease caused by a protozoa
• Karposi's sarcoma-cancer with characteristic purple lesions
• Lymphoma (certain types)-cancer of the lymphatic system
• Mycobacterium avium complex-a type of bacterial infection
• Pneumocystis carinii/jiroveci pneumonia-specific types of bacterial pneumonia
• Recurrent pneumonia
• Progressive multifocal leukoencephalopathy-destruction of the covering of the nerve cells
• Salmonella septicemia (recurrent)-a severe form of bacterial diarrhea
• Toxoplasmosis of the brain-a type of parasitic infection
• Tuberculosis-an infectious disease caused by the tubercle bacillus
• Wasting syndrome-a disease characterized by unintentional weight loss and weakness

Cancer is uncontrolled and dangerous cell growth. When the mechanisms that normally keep cell division under control fail, cells can divide too often, damage and invade surrounding tissue, and cause sickness and death. The "C-word" will touch almost every family, and it is terrifying to many people at a deep, instinctual level.

Cervical cancer is highly preventable. If she gets regular Pap smears, a diagnostic test that screens for dangerous changes in the cervix, no woman need ever die of this disease. Unfortunately, such tests aren't always available, and cervical cancer is therefore a leading cause of death for women in many developing countries. This is a particular shame, since cervical cancer is also one of very few cancers with a clearly diagnosable and measurable cause—infection with one of the cancer—causing types of human papilloma virus. Improvements in DNA analysis have led to the realization that the vast majority, if not all, cases of cervical cancer are caused by HPV. It can cause other sexually transmitted cancers as well. HPV infection is also associated with rectal, anal, and penile cancer. Hope looms on the horizon, however, since the FDA has recently approved a vaccine to prevent the most common cancer-causing forms of the virus.

Reproductive cancers are particularly devastating because people sometimes feel that these cancers damage the essence of their masculinity or femininity. Not only can these cancers cause pain during sex, but treatment can disfigure the parts of the body that many associate with sexual attraction. Chemotherapy and radiation for any cancer can cause exhaustion and hair loss, leading to feelings of loss of attractiveness or low self esteem. Losing sexual organs to cancer can be particularly devastating for some individuals. Women may ask, "Will he still love me if I only have one breast?" or "Am I still a woman if I can no longer bear children?" It can be a challenge to focus on the fact that just being alive and healthy is beautiful and sexy. We are more than the sum of our parts.

Breast cancer affects approximately one in 93 women by the age of 45, and over the course of a lifetime one in eight women will be diagnosed with the disease. Although the discovery of the breast cancer genes BRCA1 and BRCA2 was hailed as miraculous, in reality, very few cancers are caused by these genes. Women who have these genes, or women who have a family history of breast cancer, are at much higher risk for cancer and should start being screened for it earlier than women who don't. Every woman needs to go for regular mammograms (screening tests) once she reaches the age of 40. All women, even those in their 20s, should perform regular breast self-exams and have a clinical breast exam during their annual medical exam. Early detection is critical, because when breast cancer is diagnosed at an early stage, women have an excellent chance of survival—greater than 90 percent for stages zero and one combined.

Approximately 1 to 2 percent of women in the U.S. will be diagnosed with endometrial (uterine) cancer. Most endometrial cancer occurs in post-menopausal women, but between 2 to 5 percent of cases occur in women under 40. This condition is different from endometriosis, where the uterine lining grows outside of the uterus. It is characterized by malignant (cancerous) changes in the cells instead of by an abnormality in where they grow. If caught early enough, survival rates are 5 to 9 percent. Fortunately, most cases are diagnosed in an early stage since this cancer has the highly noticeable symptoms of abdominal cramping, heavy vaginal bleeding, and/or bleeding between periods. Although these symptoms are common to many other diseases as well, investigating them usually leads to efficient diagnosis.

Ovarian cancer is uncommon, with a lifetime incidence of only one in fifty women, but it is the fifth leading cause of cancer death in women. Twenty-five percent of ovarian cancer deaths occur in women between the ages of 34 and 55. The disease is so deadly because diagnosis is so difficult. Symptoms are vague, and ovarian cancers shed cells that can invade other internal organs long before the presence of disease is even suspected. More than half of all women with ovarian cancer are diagnosed at an advanced stage, and overall survival rates are only 35 to 38 percent. If the disease is caught early enough, however, the five-year survival rate is greater than 90 percent.

Male reproductive cancers hit at the extremes of age. Testicular cancer, although it represents less than one percent of all cancers in men, is the most common cause of cancer in men aged 15 to 40. Most testicular cancers are caught early, diagnosed when a man or his partner notices a change in the shape of his testicles, and the survival rates are excellent. Loss of a single testicle does not affect sexual performance, and an artificial testicle that matches the size and firmness of the original can even be inserted so that sexual appearance is maintained. Loss of two testicles will lead to infertility, but fortunately sperm can be preserved so that if men so choose, they can have children later in life. One of the most interesting things about testicular cancer is that it's one of very few diseases more common in white men than in African Americans.

Prostate cancer is the leading cause of cancer death in men over the age of 75 and the third leading cause of cancer death in men of all ages. It is primarily a disease of older men and almost never occurs in men under the age of 40. It is, in some ways, more difficult to diagnose than other cancers because almost all men experience some enlargement of the prostate as they age. This enlargement is usually benign (non-cancerous) and it can be monitored through the use of a blood test for prostate specific antigen (PSA) as well as through more invasive exams. The choice of treatment method can have profound effects on a man's health and sexual function. Early cancers are normally treated with removal of the prostate. Later cancers are often treated by removal of the testicles (termed an orchidectomy, after the Latin word for orchid, whose root the testicle resembles) to lower the level of testosterone and decrease cell growth. Removal of testosterone, however, can have negative effects on both overall health and sexual function.

Almost half of all women in the U.S. experience some form of sexual dysfunction. Sexual dysfunction in women can be caused by both psychological and biological problems, and the three most common types of sexual problems are lack of interest in sex, inability to achieve orgasm, and pain during sex. All of these problems are more common in younger women and women with less education, suggesting an important role for psychological maturity and life experience. But a great deal of sexual dysfunction in women is actually biological in origin. Sexual pain, for example, is far more strongly associated with urinary tract symptoms and other health problems than it is with emotional problems or stress, and arousal disorders are equally affected by both.

Vaginismus is an uncontrolled spasming of the outer vagina which can make penetration impossible. It can be caused by physical scarring as well as psychological difficulties, and it is interestingly one of the main causes of unconsummated marriages. Dyspareunia is defined as pain during sex in a man or a woman, not accounted for by vaginismus or lack of lubrication. The most common form of dyspareunia is vulvar vestibulitis syndrome (VVS), where women are extremely sensitive to sensation on the vulva or surrounding glands, and particularly to penetration. Studies have shown that women with VVS can perceive levels of touch that are imperceptible to other women, and that normal levels of touch to most women cause women with VVS extreme pain. Treatment for female sexual pain disorders usually involves psychological counseling as well as techniques that a woman can perform to reduce her sensitivity to penetration. Pain-reducing medications, such as tricyclic antidepressants, may also be prescribed, and some doctors have had success with biofeedback, physical therapy, and other similar treatment methods. There is no one accepted method for treating these disorders, and very few clinical trials have been performed.

Uterine fibroids are benign muscular tumors of the uterine wall. Essentially, the uterus puts out one or more extensions of itself, which can fill the uterine cavity or grow outside the wall into the abdomen. Uterine fibroids can range in size from very tiny (a quarter of an inch) to larger than a cantaloupe. Occasionally they can cause the uterus to grow to the size of a five-month pregnancy. Although they are not inherently dangerous, uterine fibroids can cause pain or make it difficult to maintain a pregnancy. Treatment ranges from ignoring them completely to hysterectomy-removal of the uterus.

Endometriosis is a common condition where the endometrium, or uterine lining, grows outside of the uterus. Depending on the extent of the disease, the symptoms of endometriosis can range from none to extreme pelvic pain. There may even be bleeding inside the abdomen, since this tissue experiences the menstrual cycle in the same way as endometrial tissue that is properly confined. More than 97 percent of pelvic pain in women is due to endometriosis. Treatment for endometriosis ranges from use of birth control pills or other hormones to try and control the growth of the tissue to surgery-which may remove either the excess endometrial tissue or the uterus itself.

Priapism is defined as a persistent or undesired erection of the penis, and it is considered to be a problem when regular sexual activity will not make it go down. It's tempting to joke that an endless erection sounds like every man's fantasy, but in fact it's very dangerous. If a man stays hard too long, he can suffer significant medical problems, including permanent damage to the erectile tissue. At some point, usually around the 4-hour mark, medical treatment becomes necessary, which can range from administration of medication to cutting holes in the penis to drain out the excess blood.

Priapism is divided into two types: low flow (ischemic) and high flow (non-ischemic.) In low-flow priapism, which is considered to be the most serious, the veins that allow blood to flow out of the penis are blocked. This is not only a painful experience—if left unrelieved, it can also cause permanent scarring and impotence. One frequent cause is sickle cell anemia, when malformed (shaped like a sickle) blood cells get stuck in the penile veins. It can also be caused by neurological problems, various medications, and certain types of infection. In high-flow priapism, blood simply flows into the penis too fast. This is normally caused by some traumatic damage to the penis, including local injection of drugs, which damage the penile arteries, leading to localized uncontrolled bleeding. It does not usually lead to permanent damage.

For men, there can be multiple sources of pelvic discomfort. Two of the most common ones are varicocele and paratesticular cysts. Varicoceles are essentially varicose veins of the spermatic cord—the structure that supports the testes inside the scrotum. Varicoceles are most commonly found in young men between the ages of 15 and 25. They tend to be located on the left side of the scrotum, probably because of the direction of circulation. They are usually minor and can be managed with the use of a scrotal support. However, if the damage is serious, lack of sufficient blood flow to the testes can result in testicular atrophy and infertility. Microsurgery is an option for the repair of varicoceles.

Cysts of the testes and surrounding tissues come in many forms, and those that occur in the scrotum (but not the actual testes) are almost always benign. Such paratesticular tumors, or cysts, are extremely common—far more so than testicular cancer. Non-cancerous tumors can involve the outer covering of the testes, the epididymis, and even the spermatic cord, and most have no symptoms. Just like testicular cancers, they are normally discovered during a manual self-examination, which men should perform at least once a month, and are very easy to mistake for cancerous lumps. This is why all testicular growths must be carefully examined by a physician, using biopsy, ultrasound, or even MRI. Although most will probably be non-cancerous cysts or other benign intra-scrotal lesions, serious disease should always be ruled out. Cancers are much more curable when caught at an early stage, and so it is essential to seek medical diagnosis for any suspicious lump sooner rather than later.