In most cases a sexually transmitted disease (STD) is passed through sexual contact, whether vaginal, anal, or oral in nature. Occasionally other methods may result in STD transmission, such as through the passing of bodily fluids with one's hands. Very rarely, certain diseases may be passed through contact with a surface on which an infected person has been.
The most common means for STD transmission is through sexual intercourse with an infected partner. Many diseases are carried in bodily fluids, especially semen or vaginal secretions. The genitals are especially vulnerable to being infected because they are comprised of very thin tissue. Friction applied during sexual encounters may also cause tears or abrasions in the skin, leading to an increased risk of infection. Saliva and blood also contain strains of certain sexually contracted diseases, meaning anal and oral sex are not any safer in the prevention of STDs.
Many times a partner does not know that he or she has contracted a sexually transmitted disease until weeks or months after the initial infection. Common symptoms are STD transmission can include cold like symptoms, unusual discharge from the penis or vagina, lesions or bumps on or around the genitals, fever, and a foul odor in the genital region. Pain upon urination, burning, itching, and redness are also common with certain diseases. Any of these symptoms should be checked out by a medical professional as soon as they appear. Many STDs are curable with prompt treatment.
The only surefire way of preventing STD transmission is by abstaining from sex, or by only having sex with one partner who does not have any sexually transmitted diseases. If this isn't possible or desires, the use of barrier birth control methods, such as condoms, is very effective at preventing certain diseases. No barrier method is 100% effective.
Human immunodeficiency virus is perhaps the most serious STD. It is passed in the same way as others, although it can also be passed through receiving tainted blood from a donor and through sharing needles with an infected person. Other diseases, such as crabs, can occasionally be spread through sitting on a surface where an infected person has been previously. STD transmission can also sometimes take place if vaginal or anal fluids are spread from one person to another with the hands during petting or sexual play.