An STD is an infection transmitted through sexual contact, caused by bacteria, viruses, or parasites. Many types of STDs exist and can impact women in different ways. Bacterial STDs include chlamydia, gonorrhea, and syphilis. Viral STDs include HIV, genital herpes, genital warts (HPV), and hepatitis B. Trichomoniasis is caused by a parasite. The germs that cause STDs hide in semen, blood, vaginal secretions, and sometimes saliva. Antibiotics, often in a single dose, can cure many sexually transmitted bacterial and parasitic infections, including gonorrhea, syphilis, chlamydia and trichomoniasis.