AIDS destroys the body’s ability to fight infections. It is the final stage of HIV infection, reached when the virus has killed so many immune cells that the body can no longer defend itself against diseases that a healthy person would easily survive. Without treatment, this process typically takes about 10 years from the initial HIV infection, and survival after an AIDS diagnosis averages around 3 years.
How HIV Attacks the Immune System
HIV targets a specific type of white blood cell called a CD4 cell (sometimes called a “helper T cell”). These cells act as coordinators of your immune response, signaling other immune cells to find and destroy invaders like bacteria, viruses, and fungi. HIV latches onto the CD4 molecule on the cell’s surface, enters the cell, and hijacks its machinery to make copies of itself. Each infected cell is eventually destroyed in the process.
The destruction happens through several pathways. Some infected cells simply burst open as new copies of the virus flood out. Others are killed by a process called pyroptosis, a highly inflammatory form of cell death that accounts for roughly 95% of CD4 cell loss. During pyroptosis, a dying cell dumps its contents into the surrounding tissue, triggering inflammation that causes neighboring cells to die the same way. This creates a chain reaction of immune cell destruction that steadily erodes your defenses over months and years.
HIV also throws the immune system into overdrive. The virus produces proteins that constantly stimulate immune cells, forcing them to divide and activate far more than normal. Activated immune cells burn out quickly, dying off at a much faster rate. So the virus attacks from two directions at once: directly killing CD4 cells and driving the immune system to exhaust itself.
What Happens as the Disease Progresses
HIV infection moves through three stages. The first, acute infection, develops within two to four weeks of exposure. Many people experience flu-like symptoms during this phase: fever, sore throat, swollen glands, rash. The virus is replicating rapidly and is highly contagious, but symptoms often pass within a few weeks.
The second stage, chronic HIV infection, can last a decade or more. During this time the virus is still active, still killing CD4 cells, but at a slower pace. Many people feel fine and have no symptoms at all. Without treatment, though, CD4 counts drop steadily. A healthy person has between 500 and 1,500 CD4 cells per cubic millimeter of blood. When that number falls below roughly 200, the immune system is critically weakened, and the person is diagnosed with AIDS.
The Infections AIDS Lets Through
AIDS itself doesn’t kill people directly. What kills is the wave of “opportunistic” infections and cancers that take hold once the immune system can no longer keep them in check. Many of these are caused by organisms that already live in or around your body, normally held in check by healthy immune function. Once that barrier falls, they can spread unchecked.
The most common and dangerous of these include:
- Pneumocystis pneumonia: a fungal lung infection that is rare in healthy people but was one of the first recognized signs of the AIDS epidemic
- Tuberculosis: a bacterial infection that can affect the lungs and spread throughout the body
- Candidiasis: a yeast infection that spreads beyond the mouth or skin into the esophagus, airways, or lungs
- Toxoplasmosis: a parasitic infection that can cause brain abscesses and seizures
- Kaposi sarcoma: a cancer that causes purple or brown lesions on the skin and internal organs
- Lymphoma: cancers of the immune system, including types that develop in the brain
- Cytomegalovirus: a viral infection that can cause blindness by attacking the retina
Chronic herpes outbreaks, recurring bacterial pneumonia, invasive cervical cancer, and persistent salmonella infections are also on the CDC’s list of AIDS-defining conditions. Any one of these can be life-threatening in a person whose immune system is too depleted to mount a response.
Effects Beyond the Immune System
AIDS doesn’t just leave you vulnerable to infections. It causes direct damage throughout the body. HIV-associated wasting syndrome, defined as unintentional loss of more than 10% of body weight combined with chronic diarrhea or fever lasting at least 30 days, was once one of the most visible signs of advanced disease. The body essentially consumes its own muscle and fat as the virus and chronic inflammation drain its resources.
The brain is also a target. HIV can cross into the central nervous system and cause a condition known as HIV encephalopathy, a form of dementia that affects movement, thinking speed, and memory. Even before reaching the AIDS stage, HIV-related brain injury can cause milder cognitive problems like difficulty concentrating or slowed mental processing. The virus triggers dysfunction in the barrier that normally protects the brain from harmful substances in the blood, allowing inflammation to take hold in brain tissue.
How Treatment Changes the Outcome
Antiretroviral therapy (ART) works by blocking HIV at multiple points in its life cycle. Some drugs prevent the virus from converting its genetic material into a form that can hijack your cells. Others stop the virus from inserting its genes into your DNA. Still others prevent infected cells from assembling new virus particles, or block the virus from attaching to and entering CD4 cells in the first place. Modern treatment combines drugs from different classes to attack the virus from several angles simultaneously, making it extremely difficult for HIV to develop resistance.
The results are dramatic. With early diagnosis and prompt treatment, the life expectancy of a person living with HIV now matches that of the general population. Treatment drives the amount of virus in the blood down to undetectable levels, which allows CD4 counts to recover and the immune system to rebuild. A person who maintains an undetectable viral load has zero risk of transmitting HIV to sexual partners, a principle known as U=U (undetectable equals untransmittable).
The global impact of expanded treatment access is visible in the numbers. In 2004, 2.1 million people died from AIDS-related illnesses worldwide. By 2024, that figure had dropped to around 630,000. That number is still far too high, driven largely by late diagnosis and inconsistent access to medication in many parts of the world. But the trajectory is clear: AIDS went from a near-certain death sentence to a manageable chronic condition for people who have access to treatment and take it consistently.