HIV infection is a chronic condition caused by a virus that attacks the body’s immune system, making it harder to fight off infections and diseases. While there is currently no cure, modern treatments allow most people living with HIV to lead long, healthy lives and protect others from transmission.

Understanding HIV Infection Worldwide

HIV infection affects millions of people across the globe. By 2022, approximately 40.4 million lives had been claimed by HIV and AIDS since the virus was first identified in 1983^[7]. Today, around 40 million people are living with HIV worldwide, with many unaware of their status^[9]. In the United States, approximately 1.2 million people are living with HIV, and roughly 32,000 Americans acquire the virus each year^[9].

The impact of HIV has changed dramatically over the past few decades. Thanks to the development and widespread availability of highly active antiretroviral therapies (medications that fight the HIV virus), HIV has transformed from a fatal diagnosis into a manageable chronic illness. People with HIV who receive proper treatment can now live long and healthy lives, similar in length to those without the virus.

Despite significant progress, HIV rates show varied patterns around the world. While global HIV and mortality rates have steadily decreased overall, some countries still report rising infection rates, often in areas experiencing political turmoil or lacking adequate healthcare resources^[7]. Certain populations remain disproportionately affected by HIV, including men who have sex with men, people who are Black or Hispanic, transgender women, and individuals who inject drugs or engage in sex work^[5][8].

What Causes HIV Infection

HIV stands for human immunodeficiency virus, which is the virus responsible for causing HIV infection. This virus belongs to a special category called retroviruses, which work backward from the way human cells normally function. Human cells store their instructions in DNA, which sends messages through RNA to make proteins. Retroviruses like HIV have their instructions written on RNA instead. When HIV invades your cells, it converts its RNA into DNA and inserts these instructions directly into your cell’s genetic material. Your cells then follow the virus’s instructions as if they were their own, producing more copies of HIV^[5].

HIV specifically targets and destroys CD4 cells, also called helper T cells, which are white blood cells crucial for fighting infections. The virus attaches itself to these cells, enters them, and uses their machinery to replicate. As HIV destroys more CD4 cells over time, the immune system gradually weakens^[4][10].

Without treatment, HIV can slowly damage the immune system until it reaches a point where the body can no longer defend itself against even minor infections. When the immune system becomes severely compromised, HIV infection progresses to AIDS (acquired immunodeficiency syndrome), the most advanced stage of infection. However, with modern treatment, most people living with HIV in developed countries do not progress to AIDS^[2][8].

How HIV Spreads Between People

HIV spreads through contact with certain body fluids from a person who has the virus. These fluids include blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk^[1][3]. For transmission to occur, these infected fluids must come into contact with a mucous membrane (found inside the rectum, vagina, opening of the penis, and mouth), damaged tissue, or be directly injected into the bloodstream.

The most common ways HIV spreads in the United States include having vaginal or anal sex without a condom with someone who has HIV, and sharing needles, syringes, or other drug injection equipment^[1][23]. Oral sex also carries some risk, though far fewer cases of HIV transmission are attributed to oral sex compared to vaginal or anal intercourse^[9].

HIV can also spread from mother to child during pregnancy, childbirth, or breastfeeding if the mother has a detectable viral load (measurable amount of HIV in the blood)^[8]. Additionally, the virus can be transmitted through sharing sex toys or tattoo and piercing needles with someone who has HIV^[8][9].

Since 1985, donated blood in many countries has been tested for HIV, making the risk of getting HIV from a blood transfusion extremely low in places with effective screening programs^[8]. Healthcare workers who accidentally prick themselves with an infected needle face a possible but very low risk of infection.

Who Is at Higher Risk for HIV

While anyone can get HIV if exposed to the virus, certain groups and behaviors increase the likelihood of infection. Understanding these risk factors helps people make informed decisions about prevention and testing.

Men who have sex with men, particularly those who engage in unprotected sex, face higher rates of HIV infection^[5][8]. This doesn’t mean HIV only affects this population, but statistical data shows they are disproportionately impacted. Similarly, transgender women experience higher HIV rates compared to the general population.

People who inject drugs and share needles, syringes, or other injection equipment are at significant risk because HIV can survive in used syringes for a month or more^[9]. Even sharing equipment used to prepare drugs, such as spoons or swabs, can transmit the virus.

Individuals with multiple sexual partners, those who engage in high-risk sexual activities, or people with other sexually transmitted infections are at increased risk^[8]. Sex workers and victims of sexual assault also face elevated risk. Having a current or previous partner with HIV increases your chances of infection, as does being from a country with high HIV rates^[8].

Certain racial and ethnic groups, particularly Black and Hispanic populations, experience disproportionately higher rates of HIV infection in the United States^[5]. This disparity often reflects broader social and economic inequalities rather than biological differences.

People who have received blood transfusions or been exposed to infected blood, tissue, or bodily fluids in countries without effective HIV screening or safe hygiene practices may also be at risk^[8]. Additionally, factors such as alcohol or drug use during sex can increase risk by affecting judgment and decision-making about protective measures like condom use^[1].

Recognizing HIV Symptoms

The symptoms of HIV vary significantly from person to person and depend on the stage of infection. Understanding what to watch for can help ensure early diagnosis and treatment, though it’s important to remember that the only way to know your HIV status for sure is to get tested.

Within two to four weeks after infection, some people develop flu-like symptoms during what’s called the primary infection or acute HIV stage^[1][3]. These symptoms can include fever, headache, muscle aches and joint pain, rash, sore throat with painful mouth sores, swollen lymph glands (particularly on the neck), diarrhea, weight loss, cough, and night sweats. This illness may last anywhere from a few days to several weeks. However, these symptoms are easily confused with other common illnesses like the flu, so having them doesn’t necessarily mean you have HIV^[1][3].

Many people experience no symptoms at all during early infection^[1][4]. This means a person can have HIV for years without knowing it, which is why testing is so crucial. During this symptom-free period, the virus continues to damage the immune system quietly, slowly destroying CD4 cells even though the person looks and feels healthy^[9].

If HIV remains untreated, it gradually weakens the immune system over time. This process can take five to ten years or sometimes longer before AIDS develops^[9][14]. As the immune system becomes severely damaged, the body becomes vulnerable to opportunistic infections—diseases that take advantage of a weakened immune system—and certain cancers. These more serious illnesses may include tuberculosis, pneumonia, or various types of cancer^[8][15].

Advanced HIV or AIDS can cause rapid weight loss, extreme tiredness, recurrent fever, prolonged swelling of lymph glands, diarrhea lasting more than a week, sores in the mouth, anus, or genitals, pneumonia, skin discolorations, and memory loss or depression^[3][14]. However, with early diagnosis and consistent treatment, most people with HIV never reach this stage.

Preventing HIV Infection

Today, more tools than ever before are available to prevent HIV transmission. Using these prevention strategies correctly and consistently can dramatically reduce or even eliminate the risk of getting or spreading HIV.

Using condoms correctly every time you have sex remains one of the most effective ways to prevent HIV and other sexually transmitted infections^[1][8]. Latex condoms provide the best protection, but polyurethane condoms work well for people with latex allergies. Using water-based lubricants with condoms is important because oil-based lubricants can cause condoms to break or tear^[8].

Pre-exposure prophylaxis, commonly called PrEP, is a medication that people without HIV can take to prevent infection. When taken as prescribed, PrEP is highly effective at reducing the risk of getting HIV through sex or injection drug use^[1][23]. PrEP is recommended for people who are at higher risk of HIV exposure.

If someone has been exposed to HIV within the past 72 hours—such as through unprotected sex, sexual assault, or sharing needles—they should seek post-exposure prophylaxis (PEP) immediately. PEP is emergency medicine that may prevent HIV infection if started quickly enough. It’s available from sexual health clinics, emergency departments, and some other healthcare settings^[8][23].

Never sharing needles, syringes, or other drug injection equipment is critical for preventing HIV among people who inject drugs^[1][8]. Many communities offer needle exchange programs where people can safely dispose of used equipment and get clean supplies. Similarly, avoiding sharing equipment for tattooing or body piercing helps prevent transmission.

For people living with HIV, taking HIV treatment as prescribed is one of the most important prevention tools. When HIV medicines reduce the amount of virus in the blood to an undetectable viral load, it becomes impossible to transmit HIV to sexual partners. This concept, often summarized as “undetectable equals untransmittable,” means that effective HIV treatment protects both the person with HIV and their partners^[1][8][15].

Pregnant women with HIV should take or continue taking HIV medicines throughout pregnancy and childbirth to prevent transmission to their babies. With proper treatment, the risk of passing HIV to the baby becomes very low^[9][23]. Women with HIV are also advised not to breastfeed in settings where safe alternatives are available, as HIV can be transmitted through breast milk.

Getting tested regularly for HIV and other sexually transmitted infections allows people to know their status and take appropriate action. Everyone between ages 13 and 64 should get tested for HIV at least once, with more frequent testing recommended for those at higher risk^[1].

How HIV Affects the Body

Understanding how HIV changes normal body functions helps explain why treatment is so important and how the disease progresses without intervention.

HIV’s primary target is the immune system, specifically the CD4 T lymphocytes that coordinate the body’s response to infections. These cells act like commanders in your immune system’s army, directing other cells to fight off invaders. When HIV infects a CD4 cell, it hijacks the cell’s machinery to produce thousands of new virus copies. This process destroys the CD4 cell^[4][10].

As HIV continues replicating and destroying CD4 cells, their numbers gradually decline. A healthy person typically has between 500 and 1,600 CD4 cells per cubic millimeter of blood. When CD4 counts drop below 200, or when certain serious infections or cancers develop, the infection has progressed to AIDS^[11]. At this stage, the immune system is severely weakened and can no longer defend against diseases that wouldn’t normally cause problems in people with healthy immune systems.

The viral load—the amount of HIV in the blood—provides important information about how active the virus is in the body. Without treatment, viral loads typically remain high, meaning the virus is actively reproducing and destroying more CD4 cells. High viral loads also increase the likelihood of transmitting HIV to others^[10].

HIV treatment works by preventing the virus from making copies of itself, which reduces the viral load and gives the immune system a chance to recover. The CD4 cell count can increase again, allowing the body to better fight off infections. When treatment reduces the viral load to an undetectable level, the immune system can function much more normally, even though HIV is still present in the body^[10][11].

Beyond the immune system, HIV can affect other parts of the body over time. The chronic inflammation caused by HIV infection may increase the risk of heart disease, kidney problems, bone loss, and certain cancers even when the virus is well-controlled with treatment^[17]. This is why people with HIV need comprehensive healthcare that addresses not just the virus but their overall health.