Viral load is the amount of HIV virus particles in the blood of someone who has HIV. The higher someone’s viral load, the more likely that person is to transmit HIV. Viral load is highest during the acute phase of HIV and without antiretroviral therapy (ART).

Taking ART daily as prescribed can make the viral load very low—so low that a test can’t detect it (called an undetectable viral load). People with HIV who keep an undetectable viral load (or stay virally suppressed) can live long, healthy lives. Having an undetectable viral load also helps prevent transmitting the virus to others through sex or sharing needles, syringes, or other injection equipment, and from perinatal transmission during pregnancy, birth, and breastfeeding.


If you have another sexually transmitted infection (STI), such as syphilis, gonorrhea, chlamydia, or herpes simplex virus (HSV), you may be more likely to get or transmit HIV. Getting tested and treated for STIs can lower your chances of getting or transmitting HIV and other STIs.

If you have HIV and get and keep an undetectable viral load, getting an STI does not appear to increase the risk of transmitting HIV. But STIs can cause other problems.

Using condoms the right way every time you have sex can reduce your chances of getting or transmitting STIs that can be passed through genital fluids, such as gonorrhea, chlamydia, and HIV. Condoms are less effective at preventing STIs that can be transmitted through sores or cuts on the skin, like human papillomavirus (HPV), HSV, and syphilis.

If you’re sexually active, you and your partners should get tested for STIs, even if you don’t have symptoms. Find out more about STIs here. To get tested for HIV or other STIs, find a testing site near you.


When you’re drunk or high, you’re more likely to engage in risky sexual behaviors like having sex without protection (such as condoms or medicine to prevent or treat HIV) or sharing injection supplies and equipment. Being drunk or high affects your ability to make safe choices.

Drinking alcohol, particularly binge drinking, and using club drugs can alter your judgment, lower your inhibitions, and impair your decisions about sex or drug use. You may be more likely to have unplanned sex, have a harder time using a condom the right way every time you have sex, have more sexual partners, or use other drugs.

If you’re going to a party or another place where you know you’ll be drinking or using drugs, you can bring condoms so that you can reduce your risk of getting or transmitting HIV if you have vaginal or anal sex.

Counseling, medicines, and other methods are available to help you stop or cut down on drinking or using drugs. Talk with a counselor or healthcare provider about options that might be right for you. To talk with someone about substance use, find a treatment center near you.


The highest risk of getting or transmitting HIV is from sharing needles, syringes, and equipment to inject drugs, hormones, steroids, or silicone. When you share needles or other equipment, there is a very high probability that blood mixing will occur. Hepatitis virus can also be transmitted by sharing needles, syringes, and other injection equipment.

The next greatest risk for HIV infection is from unprotected sexual intercourse (without a condom or medicine to prevent HIV transmission). Receptive anal intercourse carries the highest risk. The lining of the rectum is very thin and can be damaged very easily during sexual activity. This makes it easier for HIV to enter the body. The insertive partner (top) in anal intercourse seems to have a much lower risk.

Receptive vaginal intercourse has the next highest risk. The lining of the vagina is stronger than the rectum but is vulnerable to infection. Also, it can be damaged by sexual activity. All it takes is a tiny scrape that can be too small to see. The risk of infection is increased if there is any inflammation or infection in the vagina.

The risk is higher for the receptive partner. However, there is some risk for the insertive partner in anal or vaginal sex. It’s possible for HIV to enter the penis through any open sores, through the moist lining of the opening of the penis, or through the cells in the mucous membrane in the foreskin or the head of the penis.


There have been many studies of HIV transmission through oral sex. They have not come to clear conclusions. However, the following points are clear:

    • Oral sex involves putting the mouth on the penis (fellatio), vagina (cunnilingus), or anus (rimming).
    • It is possible to get or transmit HIV through oral sex, but the risk of infection is low.
    • If you or your partner has other STIs, genital sores, oral ulcers, or bleeding gums, the risk of getting or transmitting HIV from oral sex is increased.
    • You can get other STIs from oral sex.
    • If you get feces in your mouth during rimming, you can get hepatitis A virus (HAV), hepatitis B virus (HBV), parasites like Giardia, and bacteria like Shigella, Salmonella, Campylobacter, and E. coli.


Researchers have developed estimates of the risk of transmission of HIV. These estimates can give you a general idea of which activities are more or less risky. They cannot tell you that any activity is safe or how many times you can do them without getting infected. The best way to avoid getting or transmitting HIV is to use a condom correctly and consistently for all sexual activity and to avoid sharing needles and other injection equipment. If you think you have been exposed to HIV, talk to your health care provider immediately. Ask whether you can use HIV treatments to prevent infection.


CDC Risk Reduction Tool (use this tool to access tailored information about your risk of getting or transmitting HIV and how you can reduce your risk. Who is at Risk for HIV?

 Reviewed March 2021

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