AIDS (acquired immunodeficiency syndrome) is the most advanced stage of HIV infection, and its symptoms reflect a severely weakened immune system that can no longer fight off infections and diseases a healthy body handles easily. A person is diagnosed with AIDS when their CD4 cell count, a measure of immune strength, drops below 200 cells per cubic millimeter. A healthy adult typically has between 500 and 1,500. Without treatment, HIV progresses to AIDS in roughly 7 to 8 years on average, though this varies widely from person to person.
How AIDS Differs From Earlier HIV Stages
HIV infection moves through stages. In the earliest weeks, many people experience flu-like symptoms such as fever, sore throat, and fatigue as the virus rapidly multiplies. After that, the virus often enters a long, quiet phase where a person may feel fine for years while the virus slowly destroys CD4 cells. AIDS is the final stage, where the immune system is damaged enough that the body becomes vulnerable to a group of serious illnesses called opportunistic infections and certain cancers.
The symptoms of AIDS aren’t caused by HIV itself so much as by everything the immune system can no longer keep in check. That’s why AIDS symptoms are so varied: they depend on which infections or conditions take hold.
General Physical Symptoms
Several symptoms are common across many people with AIDS, regardless of which specific infections are present. These include:
- Rapid, unexplained weight loss. Wasting syndrome, one of the hallmark signs of AIDS, involves losing more than 10 percent of body weight along with diarrhea, weakness, or fever lasting at least 30 days. For someone weighing 160 pounds, that means losing 16 or more pounds without trying.
- Recurring fevers and drenching night sweats. These can persist for weeks and often don’t have an obvious cause.
- Extreme, lasting fatigue. Not the tiredness that improves with rest, but a deep exhaustion that interferes with daily life.
- Chronic diarrhea. Lasting more than a week, often contributing to the weight loss and dehydration that define wasting.
- Swollen lymph nodes. Particularly in the neck, armpits, and groin, lasting for extended periods.
Skin-Related Symptoms
The skin often shows visible signs of AIDS. Sores, rashes, and lesions that won’t heal or keep returning are common. One of the most recognizable is Kaposi sarcoma, a cancer that appears as purple, red, or brown patches or raised nodules on the skin. These lesions commonly show up on the feet, legs, and face, and can also form inside the mouth, the anus, or elsewhere in the digestive tract. They are often disfiguring and may appear in just one spot or across many areas of the body.
Other skin problems include persistent fungal infections (like severe oral thrush, which coats the tongue and inside of the mouth with white patches), shingles outbreaks that are more severe and widespread than in healthy people, and sores around the mouth or genitals that take unusually long to heal.
Respiratory Symptoms
Lung infections are among the most dangerous complications of AIDS. The most well-known is a type of pneumonia caused by a fungus that healthy immune systems easily suppress. This infection develops over days to weeks and typically causes a dry cough that doesn’t produce mucus, shortness of breath that worsens with physical activity, and a general feeling of fatigue and breathlessness. It can become life-threatening quickly if untreated, and before modern treatment existed, it was one of the leading causes of death in people with AIDS.
Tuberculosis is another serious respiratory infection that people with AIDS face at much higher rates. Persistent cough, chest pain, and coughing up blood are warning signs.
Neurological and Cognitive Symptoms
HIV can directly affect the brain and nervous system, and these effects become most pronounced during AIDS. The earliest signs tend to be subtle: difficulty concentrating, trouble following conversations, problems with memory, and a general mental fogginess that makes reading or multitasking harder than it used to be.
As the disease progresses, these cognitive changes deepen. People may develop noticeable slowness in thinking and movement, depressive symptoms, and irritability. Physical signs like tremors and changes in reflexes can appear. In its most severe form, this can progress to full dementia, with significant personality changes, confusion, and loss of the ability to function independently. Some people also develop symptoms resembling Parkinson’s disease, including stiffness and difficulty with coordination.
Headaches, confusion, and seizures can also signal a brain infection called toxoplasmosis, caused by a common parasite that a healthy immune system keeps dormant. In someone with AIDS, it can reactivate and cause swelling in the brain, leading to focal neurological problems like weakness on one side of the body or difficulty speaking.
How AIDS Is Diagnosed
AIDS is diagnosed based on a blood test measuring CD4 cells. When the count falls below 200 cells per cubic millimeter, a person with HIV is considered to have AIDS, even if they feel relatively well. A diagnosis can also be made when a person with HIV develops any of a defined list of serious conditions (including Kaposi sarcoma, certain types of pneumonia, and other opportunistic infections) regardless of their CD4 count.
For people who don’t yet know their HIV status, testing is the critical first step. Different tests have different detection windows after a potential exposure. A lab-based blood draw using a vein can detect HIV as early as 18 to 45 days after exposure. A rapid finger-stick test takes 18 to 90 days. Standard antibody tests detect HIV 23 to 90 days after exposure. The fastest option, a nucleic acid test, can find the virus as early as 10 to 33 days after exposure, though it’s not used as a routine screening tool.
What Treatment Can Do
Modern antiretroviral therapy has transformed AIDS from a death sentence into a manageable condition for most people who access treatment. These medications suppress the virus and allow the immune system to rebuild itself, leading to dramatic decreases in AIDS-related illness and death. Globally, about 630,000 people still died from AIDS-related illnesses in 2024, but this number has fallen sharply from its peak, largely because of expanded access to treatment.
Once treatment begins, most people see their CD4 counts start to rise. However, recovery varies considerably. Roughly half of people on long-term treatment may not fully restore their CD4 count above 500, and up to 16 percent may not get above the critical 200 threshold even with sustained treatment. About 20 percent of patients experience little or no immune recovery despite the virus being suppressed. Starting treatment earlier, before CD4 counts drop severely, gives the immune system the best chance of bouncing back.
One important thing to be aware of: some people experience a temporary worsening of symptoms shortly after starting treatment. This happens because the recovering immune system suddenly recognizes infections that were already present but hidden, and mounts an inflammatory response against them. This is a known reaction, not a sign that treatment is failing, though it sometimes requires medical management.