STDs can cause pain, and some can cause infertility and even death if not treated. By definition STD's are diseases contracted during sexual contact.
People can avoid STDs by changing their sexual behavior.
People with STDs, including HIV, usually do not look sick. Consistently use condoms - Use them every time and use them correctly. To prevent STDs, people at risk should use condoms even when they use another family planning method. If a woman's sex partner is not willing to use condoms, she should try to use spermicide. The diaphragm and cervical cap may also help prevent some STDs.