There are many myths and misconceptions about how long human immunodeficiency virus (HIV), the virus that causes AIDS, lives and is infectious in the air or on a surface outside the body.

Unless the virus is kept in a syringe under specific conditions, the true answer is not very long. Although it causes a serious incurable disease that can’t be inactivated by the body, HIV is very fragile in the environment outside one’s body. It quickly gets damaged and becomes inactive (“dies”) and unable to transmit infection when the fluid it’s in is exposed to air. Once it’s inactive, HIV can’t become active again, so it’s the same as if it’s dead.

HIV spreads when blood or certain body fluids that have high amounts of active virus (semen, vaginal fluids, rectal fluids, or breast milk) are exposed to one’s bloodstream. For a person to become infected, there must be enough active virus in the fluid that encounters the bloodstream. This occurs through a mucus membrane (“moist skin” such as in the mouth, rectum, penis, and vagina), a significant opening in the skin, or injection. Transmission of the virus most often happens during anal or vaginal sex, but it also occurs by sharing needles.

Factors that affect the survival of HIV outside the body include:

  • Temperature. HIV stays alive and active when kept in the cold but is killed by heat.
  • Sunlight. Ultraviolet light in sunshine damages the HIV virus so it’s no longer able to reproduce.
  • Amount of virus in the fluid. Generally, the higher the level of HIV virus in the fluid, the longer it will take for all of it to become inactive.
  • Level of acidity. HIV survives best at a pH around 7 and becomes inactive when the environment is even just a little more or less acidic.

When any of these factors aren’t perfect for HIV in its environment, survival time of the virus goes down.

HIV can’t survive for long in the air. As soon as fluid leaves the body and is exposed to air, it quickly begins to dry up. This damages the virus, making it inactive. Once it’s inactive, HIV is “dead” and no longer infectious.

Studies show that, even at levels much higher than usually found in the body fluids and blood of people with HIV, 90 to 99 percent of the virus is inactive within hours of being exposed to air.

When a bodily fluid containing HIV leaves the body and lands on a surface, such as a counter or toilet seat, the virus remains active within the fluid for several days, even as the fluid dries. The virus gradually dies over the course of several days. However, it’s important to note that the amount of virus able to transmit an infection in such a small volume is negligible, and a case of transmission from a surface (such as a toilet seat) has never been reported.

There’s nothing special about semen (or vaginal fluids, rectal fluids, or breast milk) that protects HIV so it can survive longer outside the body. As soon as any of the fluids that contain HIV leave the body and are exposed to air, the fluid dries up and inactivation of the virus starts.

HIV in blood from something like a cut or nosebleed can be active for several days, even in dried blood. The amount of virus is small, though, and unable to easily transmit infection.

Extension of the survival time of HIV in fluid outside of the body can occur when a small amount is left in a syringe used to inject drugs. After an injection in someone with high levels of HIV, enough blood stays in the syringe to transmit the virus. Since it’s inside a syringe, the blood isn’t as exposed to air as it is on other surfaces.

According to the Centers for Disease Control and Prevention (CDC), when the temperature and other conditions are just right, HIV can live as long as 42 days in a syringe, though this typically involves refrigeration. HIV lives the longest in a syringe at room temperature, but can still live up to seven days at higher temperatures.

One study showed that after 1 to 2 hours in tap water, only 10 percent of the HIV virus was still active. After 8 hours, only 0.1 percent was active. This shows that HIV doesn’t survive long when exposed to water.

Except under very specific conditions, HIV stays active and able to cause an infection for only a very short time once it leaves the body. Because there’s so much misinformation about the risk of getting HIV through casual contact with infected fluids on surfaces or the air, the CDC states specifically that HIV can’t be transmitted by air or water or by sitting on a toilet.

In fact, except for sharing needles and syringes, there has never been a documented case of a person getting HIV from casual contact with infected fluid on a surface in the environment.