You've been in a monogamous relationship for years. You and your partner have discussed your sexual histories. And you go to the doctor for regular checkups. There's no way you could be carrying or spreading a sexually transmitted disease, right? Well, not so fast.

As it turns out, many sexually transmitted diseases (STDs) are hard to spot. Some may have no symptoms at all, while in other cases, the signs could remain dormant for up to a decade. How can you avoid catching or spreading these silent diseases? Follow our guide to pinpoint and prevent the top three offenders.

The Disease: Chlamydia:

According to the Centers for Disease Control and Prevention (CDC), chlamydia is the most frequently reported bacterial STD in the United States. Although more than a million chlamydial infections were reported in the United States in 2006, the majority of cases go unreported, largely because about three-quarters of affected women and about half of affected men don't realize they've been infected. If left untreated, the disease can result in pelvic inflammatory disease (PID), chronic pain, potentially fatal ectopic pregnancies, or infertility.

The Symptoms of Chlamydia:

In some cases, symptoms may occur within one to three weeks after exposure. In women, these may include abnormal vaginal discharge, a burning sensation while urinating, lower abdominal pain, lower back pain, nausea, fever, pain during intercourse, or bleeding between menstrual periods. Men might experience discharge from the penis, a burning sensation while urinating, or burning and itching around the opening of the penis.

How to Protect Yourself Against Chlamydia:

Although abstinence is the best protection against any venereal disease (VD), latex male condoms, if used consistently and correctly, can reduce the risk of transmission. To find the disease in its earliest stages, the CDC recommends yearly chlamydia testing for all sexually active women age 25 or younger, as well as for older women with risk factors for infections (those who have a new sex partner or multiple sex partners). In addition, all pregnant women should be checked.


The Disease: Genital Herpes:

Another common STD, genital herpes is caused by the type 1 or type 2 herpes simplex virus (HSV). According to the International Herpes Alliance, up to 60 percent of people who have a genital HSV infection are unaware that they're infected and that they may be transmitting the virus to others. There is currently no cure for genital herpes, and complications may include psychological distress and an increased risk for HIV. In addition, mothers who are infected with herpes may transmit potentially fatal infections to their babies.

The Symptoms of Genital Herpes:

When symptoms occur following initial exposure, they can range from very mild to quite pronounced. The most common sign is a sore or several sores around the genitals or rectum, which typically take two to four weeks to heal. Other symptoms may include fever, swollen glands, or fatigue.

How to Protect Yourself Against Genital Herpes:

In addition to abstinence, which is the surest form of protection, latex condoms may be helpful in reducing the risk of transmission. In addition, people with herpes should always abstain from sexual activity with uninfected partners during an outbreak. Although a positive HSV-2 blood test can indicate a genital herpes infection, a negative result doesn't necessarily mean a person isn't infected with HSV.


The Disease: HPV/Genital Warts:

According to the CDC, human papillomavirus (HPV) is the most common sexually transmitted infection in the United States. The term HPV actually refers to more than 40 virus types that infect the skin and mucous membranes in the genital area. Although many people with HPV do not experience health complications, certain strains of the virus can lead to genital warts, while others can cause cancers of the cervix, vulva, vagina, anus, or penis.

The Symptoms of HPV/Genital Warts:

In some cases, HPV may result in warts (small bumps or clusters of bumps in the genital area) within a few weeks or months of exposure. These warts may appear on the vulva; in the vagina or anus; or on the cervix, penis, scrotum, groin, or thigh. But in most instances, the virus is invisible, and most people with HPV do not experience any symptoms.

How to Protect Yourself Against HPV/Genital Warts:

As with most sexual diseases, abstinence provides the greatest degree of protection against HPV, although latex condoms may help to reduce your risk. In addition, the U.S. Food and Drug Administration (FDA) has approved the HPV vaccine, Gardasil, for girls and women ages 9 to 26. It works best for those who have not previously been infected with any of the four HPV types covered by the vaccine (6, 11, 16, and 18). When administered correctly, the vaccine is 95 to 100 percent effective in preventing these types of HPV, according to the FDA.