HIV Overview

How can HIV be transmitted?

The human immunodeficiency virus (HIV) is a virus that spreads through certain body fluids. Once someone has HIV, the virus remains in the body and can be transmitted to others through these fluids:

• Blood
• Semen (including preseminal fluid)
• Vaginal fluids
• Rectal fluids
• Breastmilk

If a person has enough of the virus in their body, either because they are not taking HIV medicine (known as antiretroviral therapy, or ART) or their medicine is not working effectively, they can pass the virus to others through any of the fluids above.

How does HIV spread?

HIV is most commonly spread through unprotected vaginal or anal sex. According to the Centers for Disease Control and Prevention (CDC), sexual contact accounts for at least 89 percent of all new HIV diagnoses.

However, HIV can still be transmitted through other means, including—

• Shared needles or drug injection equipment: HIV can spread when people share needles (for drug injection, tattoos, or piercings) or other drug injection equipment that are contaminated with contagious blood.
• Perinatal HIV transmission: Babies can be exposed to HIV while breastfeeding or through contaminated blood during pregnancy and childbirth, especially if ART is not taken during or after pregnancy.
• Medical settings: HIV can be transmitted through blood transfusions or accidental needle sticks, but these are uncommon in the United States due to strict safety measures.
• Other blood exposures: In extremely rare cases, HIV can be spread by sharing personal items like a razor or toothbrush, by eating pre-chewed food from someone with HIV, or by accidental exposure to blood from an open wound of someone with HIV. These situations would require a large amount of blood (more than usual) and a direct way for it to enter the body (such as an open sore or cut).

While it is possible to transmit HIV through all of the means above, the likelihood of transmission depends on several different factors.

How likely is HIV transmission?

The chances of transmitting HIV vary based on a number of factors. Most importantly, HIV can only be transmitted through sex if someone has a detectable viral load. There is virtually no risk of transmitting HIV through sex if someone with HIV is treated and has an undetectable viral load. 

Simply, if someone is taking their HIV medicines and the medicines are working as they are intended, they cannot spread HIV to others through sex. This is known as Undetectable = Untransmittable or U=U. Learn more about how HIV treatment works in HIV Treatment: The Basics.

The U=U concept applies specifically to HIV transmission through sex. However, having an undetectable viral load greatly lowers the chance of passing HIV through other routes, like during childbirth or by sharing needles.

If someone is not treated for HIV or the HIV medicines are not working as intended, then transmission is more likely. As noted above, HIV is most commonly spread through condomless sex, but the chances of transmission vary based on the type of sex. According to the CDC, the estimated risk of HIV transmission per 10,000 exposures is—

• 138 (1.38%) for receptive anal sex
• 11 (0.11%) for insertive anal sex
• 8 (0.08%) for receptive penile-vaginal sex
• 4 (0.04%) for insertive penile-vaginal sex
• Rare but not impossible for receptive or insertive oral sex

Importantly, the numbers above only apply when exposure happens with someone who has a detectable viral load.

In the United States, the chances of HIV transmission through means other than sexual activities are the highest through perinatal transmission or via shared needles. For instance, the estimated risk of HIV transmission through shared needles during injection drug use is 63 in 10,000 exposures, nearly eight times the odds of transmission through vaginal sex.

Aside from the means above, the chances of transmitting HIV are relatively low in the United States. For instance, the per-exposure risk of HIV transmission is the highest through blood transfusions with contaminated blood, but strict screening protocols minimize that risk to less than one in a million in the United States.

In what ways can HIV not be transmitted?

There are many misconceptions about how HIV can be transmitted. HIV cannot be transmitted through—

• Casual contact:
  • Hugging
  • Kissing (closed mouth)
  • Shaking hands
• Environmental surfaces or items:
  • Air
  • Door handles
  • Shared food, drinks, or utensils
  • Swimming pools
  • Toilet seats
• Body fluids:
  • Mucus (including when coughing or sneezing)
  • Saliva
  • Sweat
  • Tears
  • Urine
• Insects or animals:
  • Ticks, mosquitoes, or other insects
  • Dogs, cats, or other household animals

There may be extremely rare exceptions to the above list if large amounts of blood are present. For example, HIV is not spread through saliva, but if contaminated blood is mixed with saliva due to an injury, bleeding gums, or open sores, transmission could be possible (although unlikely).

What increases the likelihood of HIV transmission?

When someone is untreated or has an HIV treatment regimen that is not working effectively, some behaviors can further increase the chances they will spread HIV to others. Such behaviors include—

• Having sex without a condom
• Having multiple sex partners
• Having untreated sexually transmitted infections (STIs), such as genital herpes
• Having unprotected sex with a partner who has untreated STIs
• Having a high viral load
• Using drugs that impact judgment or decision-making
• Sharing needles or drug injection equipment

What prevents HIV transmission?

Taking HIV medicines as scheduled is the most effective way to prevent spreading HIV to others. In addition, regular viral load testing can help to make sure a treatment regimen continues to be effective over time.

For those who are not treated, struggle to take HIV medicines as prescribed, or are taking a treatment regimen that isn’t working effectively, HIV transmission can be prevented by—

• Practicing safer sex practices like using a condom correctly every time you have sex
• Having a partner take pre-exposure prophylaxis before a possible exposure
• Having a partner take post-exposure prophylaxis after a possible exposure
• Disclosing your HIV status to others, particularly sexual partners

Otherwise, for people who are sexually active and may not know their HIV status, regular testing is an important way to help prevent the spread of HIV. Since HIV often has no symptoms, it can unknowingly be transmitted to others.

This fact sheet is based on information from the following sources:

From CDC:

• How HIV Spreads
• HIV Diagnoses, Deaths, and Prevalence
• Living with HIV
• Undetectable = Untransmittable

From World Health Organization:

• HIV/AIDS