Men get AIDS by first contracting HIV, the virus that causes it. HIV enters the body through specific routes: unprotected sex (anal or vaginal), sharing needles, and less commonly through blood exposure. Without treatment, HIV gradually destroys immune cells over 10 to 15 years until the immune system is too weak to fight off infections, which is the stage known as AIDS.
HIV and AIDS Are Not the Same Thing
AIDS is not something you “catch.” You contract HIV, and AIDS is what can eventually happen if the virus goes untreated. HIV attacks a specific type of immune cell called CD4 cells. A healthy person has roughly 500 to 1,500 of these cells per cubic millimeter of blood. When that count drops below 200, or when certain serious infections take hold because the immune system is too weak to fight them, the diagnosis changes from HIV to AIDS (also called stage 3 HIV).
Without treatment, signs of HIV-related illness typically develop within 5 to 10 years, and the progression to AIDS takes about 10 to 15 years. With modern treatment, most people with HIV never develop AIDS at all.
How Men Contract HIV Through Sex
Sexual transmission is the most common route for men. The risk varies dramatically depending on the type of sex and your role in it. The CDC estimates these per-act risks when no condoms, PrEP, or treatment are involved:
- Receptive anal sex (bottoming): roughly 1 in 72 acts, making it the highest-risk sexual activity by a wide margin
- Insertive anal sex (topping): roughly 1 in 909 acts
- Insertive vaginal sex: roughly 1 in 2,500 acts
These are averages. The actual risk in any single encounter shifts depending on factors like whether the HIV-positive partner has a high viral load, whether other sexually transmitted infections are present (which create openings in tissue), and whether there’s any bleeding or tearing during sex.
Receptive anal sex carries the highest risk because the lining of the rectum is a single cell layer thick and rich in the types of immune cells HIV targets. It tears easily during intercourse, giving the virus direct access to the bloodstream. Insertive partners face lower but real risk: HIV can enter through the urethra and, in uncircumcised men, through specialized immune cells concentrated in the foreskin.
Non-Sexual Transmission Routes
Sharing needles or syringes is the second most common way men contract HIV. Blood remaining in a used needle can carry a high concentration of the virus, and injecting it puts HIV directly into the bloodstream, bypassing all of the body’s external defenses.
Other routes exist but are far less common. These include occupational needle sticks (relevant for healthcare workers), blood transfusions with unscreened blood (extremely rare in countries with modern screening), and mother-to-child transmission during birth or breastfeeding. HIV is not spread through saliva, sweat, casual contact, sharing food, or insect bites.
Why Circumcision Affects Risk
Circumcised men have a roughly 60% lower risk of acquiring HIV through vaginal sex with women, based on evidence from randomized controlled trials that led the WHO to recommend voluntary male circumcision as a prevention strategy in high-prevalence areas. The inner foreskin contains a high density of Langerhans cells, a type of immune cell that HIV exploits as an entry point. Removing the foreskin eliminates that vulnerable tissue and also reduces the moist environment where the virus can survive longer. This protection applies specifically to vaginal sex; the data on anal sex is less clear.
What Happens After HIV Enters the Body
Within 2 to 4 weeks of infection, many men experience an acute illness that feels like a bad flu: fever, swollen lymph nodes, sore throat, rash, muscle aches. This phase is easy to dismiss or mistake for something else, which is one reason HIV often goes undiagnosed early on. During this acute stage, viral levels in the blood are extremely high, making the person highly contagious.
After the initial illness passes, HIV enters a long period where it continues replicating and slowly killing CD4 cells, often with no obvious symptoms. This clinically silent phase can last years. Eventually, without treatment, the immune system weakens to the point where the body can no longer fight off infections it would normally handle easily. Pneumonia, certain fungal infections, specific cancers like Kaposi sarcoma, and severe weight loss are among more than 20 conditions classified as AIDS-defining illnesses.
How Treatment Changes the Picture
Modern antiretroviral therapy changes HIV from a fatal diagnosis to a manageable chronic condition. When a person with HIV takes medication consistently and achieves what’s called an “undetectable” viral load, the amount of virus in their blood is too low for standard tests to measure. At that point, according to the CDC, the risk of transmitting HIV to a sexual partner is zero. This principle is known as Undetectable = Untransmittable, or U=U.
This matters for transmission in both directions. If your partner is living with HIV and is on effective treatment with an undetectable viral load, sex with that person carries no HIV risk.
Prevention Options for Men
PrEP (pre-exposure prophylaxis) is a medication taken by HIV-negative people before potential exposure. It’s available as a daily pill or as an injection given every two months, and it dramatically reduces the chance of getting HIV from sex or injection drug use. PrEP is widely recommended for men who have sex with men, people with an HIV-positive partner, and anyone whose sexual activity puts them at elevated risk.
PEP (post-exposure prophylaxis) is an emergency option taken after a potential exposure. It must be started within 72 hours of exposure, and sooner is better. PEP involves taking antiretroviral medication for 28 days. It’s intended for situations like a condom breaking during sex with someone who may have HIV, or an accidental needle stick.
Condoms remain highly effective at preventing HIV when used consistently and correctly. Combining condoms with PrEP offers the strongest protection available outside of abstinence. Regular HIV testing, at least annually for sexually active men and every 3 to 6 months for men at higher risk, catches infections early when treatment is most straightforward and prevents unknowing transmission to partners.