For several years after exposure to human immunodeficiency virus (HIV), an infected person will typically have either no symptoms or only minor ones such as chronically swollen lymph nodes. However, despite the absence of noticeable symptoms, HIV may be silently causing damage.
HIV infects and kills certain white blood cells called CD4 lymphocytes, reducing their number. The number of CD4 cells usually declines over time in an HIV-infected person. CD4 lymphocytes act as the 'on switch' for part of the immune system, so as the number of CD4 cells drops, damage to the immune system may progress.
Over time, individuals become increasingly susceptible to infections caused by organisms that are usually controlled by people with adequate immune systems. Those infections are called opportunistic infections.
Years after infection, HIV-infected people may develop symptoms such as night sweats, chronic diarrhea, fatigue, fever, and various skin problems. These symptoms vary in severity for each individual. If the individual receives no treatment and further immune impairment occurs, the body becomes susceptible to life-threatening complications.