What Is AIDS?

A chronic and potentially life-threatening condition caused by HIV infection

"HIV" stands for "human immunodeficiency virus, a virus that attacks causes disease by killing defensive immune cells and leaving the body vulnerable to an ever-widening host of infections that it would otherwise be able to control.

"AIDS" stands for "acquired immunodeficiency syndrome," the most advanced stage of HIV infection in which the immune system is considered compromised. Without the immune defenses to ward off disease, a person with AIDS can develop severe and potentially life-threatening infections.

As straightforward as the definitions might seem, understanding when AIDS starts and what it actually means in terms of the risk of disease is a bit more complicated.


Understanding HIV and AIDS

HIV: The Virus That Causes AIDS

HIV was first isolated in the early 1980s after public health officials in New York City and Los Angeles reported an outbreak of rare diseases among gay men. These diseases were generally not seen in young, healthy people.

Scientists soon discovered that the virus, initially dubbed "HTLV-3," was able to rapidly kill defensive immune cells and, by doing so, leave a person susceptible to infectious organisms that usually do not cause disease.

As scientists gained a greater understanding of how the virus worked, they renamed it human immunodeficiency virus, or HIV.

HIV is classified as a retrovirus, a rare group of viruses that uses RNA as its genetic material. When a retrovirus infects a host cell, it uses certain enzymes to turn its single-stranded RNA into double-stranded DNA. Once the DNA is inserted into the host cell's nucleus, it effectively "hijacks" the cell's genetic machinery and turns it into an HIV-producing factory.

HIV causes disease by targeting a type of white blood cell called a CD4 T cell lymphocyte. While these "helper" cells do not kill disease-causing organisms like HIV, they are responsible for activating and coordinating the immune response (including disease-specific adaptive immunity).

How HIV Causes Disease

As HIV targets and kills more and more CD4 T cells, the body becomes less and less able to mount an immune defense. When this happens, infections that the body would otherwise be able to control can suddenly cause disease. These are referred to as opportunistic infections.

Defining AIDS

In the early days of the AIDS epidemic, scientists began to see patterns in how diseases developed in people with HIV. Because HIV was largely confined to gay men, the cluster of opportunistic infections was initially dubbed gay-related immunodeficiency (GRID). When it became clear that other groups could get infected through sex and injecting drug use, the syndrome was renamed AIDS.

Certainly, very early on, HIV and AIDS were largely considered synonymous given that the progression of the disease was rapid and there was no form of treatment able to slow its progression.

But even then, scientists understood that the route from infection to illness was not a straight line and that a clear definition of AIDS was needed to provide healthcare providers with a road map of what to expect and how to intervene.

As epidemiological data was compiled, it became clear that the bulk of serious opportunistic infections occurred when the number of CD4 T cells dropped below 200 cells per cubic millimeter (cells/mm3). By contrast, a normal CD4 count is between 500 and 1,200 (or higher).

However, at the same time, there were plenty of people with CD4 counts above 200 who developed potentially life-threatening infections. This made experts question whether a definition focused purely on the CD4 count was sufficient.

In response, the Centers for Disease Control and Prevention (CDC) issued a definition of AIDS in 2014 that largely remains intact today.

CDC Definition of AIDS

According to the CDC, AIDS is diagnosed when:

List of AIDS-Defining Conditions

The CDC issued the first list of AIDS-defining conditions in 1987. That list was expanded in 1994 and then again in 2008, in part to include severe opportunistic commonly seen in children with HIV.

Today, the CDC lists 27 different AIDS-defining conditions in people with HIV:

AIDS and Death

In the 1980s and into the early 1990s, an AIDS diagnosis was considered by many to be a death sentence. It was only with the introduction of highly active antiretroviral therapy (HAART) in 1996 that the outlook changed. With this new form of combination therapy, scientists were able to fully suppress the virus and slow disease progression.

During the height of the epidemic in the United States, HIV was the eighth leading cause of death overall. By the mid-1990s, it accounted for 23% of deaths among men ages 25–44 and 11% of deaths among women of the same age group.

By 1995, the HIV mortality rate had peaked to its highest level ever, killing nearly 50,000 U.S. citizens and residents. With the introduction of HAART, now referred to simply as antiretroviral therapy, the death rate plummeted by more than 50% within a span of three years.

Today, people with HIV who are diagnosed and treated early can expect to live normal to near-normal life expectancies.

Even people clinically diagnosed with AIDS (diagnosed based on signs and symptoms) can enjoy longer, healthier lives once antiretroviral treatment is started. With that said, the lower your CD4 count is at the start of therapy, the less likely you will be to achieve complete immune recovery.

Today, people living with HIV are more likely to die of non-HIV-related diseases, including cancers, than HIV-related ones⁠—many of which occur 10–15 years before people in the general population. Even so, antiretroviral therapy can cut the risk of both HIV- and non-HIV-related illness by half if started early (ideally before the CD4 count dips below 500).

How the Definition Changed

Since the last revision of the list of AIDS-defining conditions was issued in 2008, the CDC definition of AIDS has remained largely unchanged. What has changed is how the definition is used.

Back in the 1980s and early-1990s, the CDC's definition of AIDS was used to establish when a person was eligible for Social Security disability and other forms of financial or medical assistance. Because an AIDS diagnosis was still associated with a high risk of death, having a CD4 count of 200 was often enough to establish a person as permanently disabled.

The same criteria would not apply today. Because HIV is now considered a chronically managed condition (long-lasting but able to be treated), people who meet the definition of AIDS will need to undergo a case-by-case evaluation to determine if they are, in fact, disabled under the terms of the law.

At the same time, healthcare providers are using the term "AIDS" less and less today—in part because of the fluidity of the definition, but also because the prognosis for many AIDS-related conditions has improved dramatically over time. If anything, the term is used more for surveillance purposes (to closely watch for) than anything else.

On top of this, "AIDS" remains a highly stigmatized term, and, in its place, many healthcare providers and advocates prefer the term "advanced HIV infection" when describing the stage of the disease.

AIDS Prevention

Antiretroviral therapy is the one intervention that can halt disease progression and reduce the risk of HIV-associated illness in people with HIV. The drugs used today are not only more effective than those of the past, but also have fewer side effects and are less prone to early drug resistance.

Some combination therapies have even been formulated to allow once-daily, single-pill dosing.

But the pills only work if you take them. And in the United States, this has become a far greater challenge than many people realize.

Of the roughly 1.2 million people living with HIV in the United States, only 66% have received HIV-specific care and only 54% have achieved complete viral suppression while on treatment. This leaves nearly a half million people vulnerable to otherwise avoidable illnesses.

While stigma plays a key role in these statistics, the lack of access to quality healthcare and misconceptions about HIV and HIV therapy continue to drive people away from highly effective, lifesaving treatment as well.

Improvement in public health messaging—as well as advances in HIV treatment—hope to reverse these trends. This includes the development of simpler therapies like Cabenuva (cabotegravir/rilpivirine), an injectable combination drug approved in 2021 that only requires once-monthly dosing.

Other interventions, like HIV pre-exposure prophylaxis (PrEP), can reduce a person's risk of getting HIV by up to 99% if taken as prescribed. Advances like these may further reduce the fear surrounding HIV and might one day resign the term "AIDS" to the history books.

A Word From Verywell

HIV is not the same disease it was even 15 years ago. With appropriate treatment, people with HIV are at far lower risk of ever developing AIDS-related illnesses. Not only can they enjoy long, healthy lives, but they can even explore pregnancy and parenthood.

And the benefits of treatment extend well beyond the person living with HIV. By achieving and sustaining an undetectable viral load, the likelihood of infecting others is reduced to zero. In short, by protecting your good health with consistent antiretroviral therapy, you also protect those around you.

Frequently Asked Questions

  • How is HIV diagnosed?

    HIV is diagnosed with a blood test that is able to detect antibodies produced by the immune system in response to the virus. There are traditional in-office tests, rapid tests, and even at-home HIV tests.

  • How is HIV treated?

    HIV is treated with antiretroviral therapy. Antiretroviral therapy involves a combination of two or more drugs that block specific stages in the virus's life cycle. By blocking viral replication, the virus is suppressed to undetectable levels, at which it can do little harm.

  • How many people die of AIDS?

    There are around 38 million people living with HIV worldwide. In 2019, nearly 700,000 died as a result of HIV-related complications. In the United States, around 5,000 deaths were attributed to HIV in 2018.

Was this page helpful?
31 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Battistini Garcia SA, Guzman N. Acquired immune deficiency syndrome. In: StatPearls [Internet].

  2. Selik RM, Mokotoff ED, Branson B, Owen SM, Whitmore S, Hall HI. Revised surveillance case definition of HIV infection -- United States. Morbid Mortal Weekly Rep MMWR.

  3. Department of Health and Human Services. A timeline of HIV/AIDS.

  4. Gallo R, Willems L, Tagaya Y. Time to go back to the original name. Front Microbiol. 2017;8:1800. doi:10.3389/fmicb.2017.01800

  5. Naif HM. Pathogenesis of HIV infection. Infect Dis Rep. 2013 Jun 6;5(Suppl 1):e6. doi:10.4081/idr.2013.s1.e6

  6. Justiz AA, Naik R. HIV-1 associated opportunistic infections. In: StatPearls [Internet].

  7. Verma AS, Kumar V, Saha MK, Dutta S, Singh A. HIV: biology to treatment. NanoBioMedicine. 2019 Sep 25;167-97. doi:10.1007/978-981-32-9898-9_7

  8. MedlinePlus. CD4 lymphocyte count.

  9. Centers for Disease Control and Prevention. Revision of CDC surveillance case definition of acquired immunodeficiency syndrome. Morbid Mortal Weekly Report MMWR.

  10. Centers for Disease Control and Prevention. revised classification system for human immunodeficiency virus infection in children less than 13 years of age. Morbid Mortal Weekly Rep

  11. Centers for Disease Control and Prevention. Appendix A: AIDS-defining conditions. Morbid Mortal Weekly Rep MMWR.

  12. Tseng A, Seet J, Phillips EJ. The evolution of three decades of antiretroviral therapy: challenges, triumphs and the promise of the future. Br J Clin Pharmacol. 2015 Feb;79(2):182-94. doi:10.1111/bcp.12403

  13. Centers for Disease Control and Prevention. Updated: mortality attributable to HIV infection among persons aged 25-44 -- United States. Morbid Mortal Weekly Rep MMWR.

  14. Brady MT, Oleske JM, Williams PL, et al. Declines in mortality rates and changes in causes of death in HIV-1-infected children during the HAART eraJ Acquir Immune Defic Syndr. 2010;53(1):86-94. doi:10.1097/QAI.0b013e3181b9869f

  15. Marcus JL, Chao CR, Leyden WA, et al. Narrowing the gap in life expectancy between HIV-infected and HIV-uninfected individuals with access to careJ Acquir Immun Defic. 2016;73(1):39-46. doi:10.1097/QAI.0000000000001014

  16. Darraj M, Shafer LA, Chan S, Kasper K, Keynan Y. Rapid CD4 decline prior to antiretroviral therapy predicts subsequent failure to reconstitute despite HIV viral suppression. J Infect Public Health. Mar-Apr 2018;11(2):265-9. doi:10.1016/j.jiph.2017.08.001

  17. Chao C, Leyden W, Xu L, et al. Exposure to antiretroviral therapy and risk of cancer in HIV-infected personsAIDS. 2012;26(17):2223-31. doi:10.1097/QAD.0b013e32835935b3

  18. INSIGHT START Study Group, Lungren JD, Babiker AG, Gordin F, et al. Initiation of antiretroviral therapy in early asymptomatic HIV infectionN Engl J Med. 2015 Aug 27;373(9):795-807. doi:10.1056/NEJMoa1506816

  19. Hanass-Hancock J, Nixon SA. The field of HIV and disability: past, present, and future. J Int AIDS Soc. 2009;12:28. doi:10.1186/1758-2652-12-28

  20. Social Security Administration. Providing medical evidence for individuals with human immunodeficiency virus (HIV) infection.

  21. POZ Magazine. Is it time for an end of 'AIDS'?

  22. Bai RJ, Dai LL, Wu H. Advances and challenges in antiretroviral therapy for acquired immunodeficiency syndrome. Chin Med J. 2020 Dec 5:23:2775-7. doi:10.1097/CM9.0000000000001226

  23. HIV.gov. What is the HIV care continuum?

  24. Food and Drug Administration. FDA approves first extended-release, injectable drug regimen for adults living with HIV.

  25. Centers for Disease Control and Prevention. How effective is PrEP?

  26. Mandelbrot L, Tubiana R, Le Chenadec J, et al. No perinatal HIV-1 transmission from women with effective antiretroviral therapy starting before conceptionClin Infect Dis. 2015 Dec;61(11):1715-25. doi:10.1093/cid/civ578

  27. Rodger A., Cambiano V, Bruun T, et al. Risk of HIV transmission through condomless sex in serodifferent gay couples with the HIV-positive partner taking suppressive antiretroviral therapy (PARTNER): final results of a multicentre, prospective, observational study. Lancet. 2019 May 2; pii: S0140-6736(19)30418-0. doi:10.1016/S0140-6736(19)30418-0.

  28. Centers for Disease Control and Prevention. Types of HIV tests.

  29. Department of Health and Human Services. Guidelines for the use of antiretroviral agents in HIV-1-infected adults and adolescents.

  30. UNAIDS. Global HIV & AIDS statistics — fact sheet.

  31. Centers for Disease Control and Prevention. AIDS and HIV.