■Hepatitis (Viral hepatitis A, B, or C)

Besides feeling sluggish there are often no symptoms, although a very small percentage (1~2%) of individuals may experience the sudden onset of heavy symptoms. Liver cirrhosis or liver cancer are common (future) complications. Hepatitis A is transmitted through fecal contact, so you need to be careful during rimming and anal sex. Hepatitis B and C are transmitted through blood and semen, so you can be infected through oral sex or intercourse.
Incubation period: Hepatitis A: 2~6 weeks, B: 1~6 months, C: 2~16 weeks (there are also people in whom the outbreak can take much longer or who never experience symptoms)

■HIV/AIDS

HIV (Human Immunodeficiency Virus) is transmitted when a mucuous membrane or damaged tissue comes into direct contact with the semen, blood, vaginal secretion, or breast milk of an infected individual. HIV gradually weakens the immune system and causes AIDS.
Incubation period: Without treatment, from the time of infection to the outbreak of the illness, about 10 years.
Treatment: Although no treatment has yet been developed that will completely get rid of the virus, the sooner you learn of your infection, the sooner the progression of the illness can be slowed down with treatment.

■Things without symptoms

Trichomoniasis: Men will show no symptoms, but women will experience a strong-smelling discharge (the discharge will smell like fish or squid!). In men the urethra will be infected, and in women the vagina will be infected.
Incubation period: 3 days~1 month
Treatment: With either liquid medication or a pill (which you place inside the vagina), the infection will heal in about 10 days. After 2 days of treatment, you won’t be contagious anymore.