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What is the risk of infection from someone else’s blood?

There are some infections that can be passed on in blood or body fluids that can become mixed with blood, such as saliva. These are known as blood-borne viruses (BBVs).

The risk of an infection being passed on in this way largely depends on the type of infection and how you come into contact with the infected blood.

Which infections can be passed on?

The main infections that can be passed on in blood are:

Of these, hepatitis B is most likely to be spread through blood, and HIV is the least likely.

These viruses can also be found in body fluids other than blood, such as semen, vaginal secretions and breast milk. Other body fluids such as urine, saliva and sweat only carry a very small risk of infection, unless they contain blood.

However, the presence of blood is not always obvious, and it is possible for someone to have one of these infections without realising it.

Routes of transmission

The chance of an infection being passed on in someone else’s blood also depends on how you come into contact with the infected blood. This is known as the route of transmission. The risks associated with different routes of transmission are outlined below.

Higher risk of infection

The risk of an infection being passed on is highest if your skin is broken or punctured as you come into contact with the infected blood. For example, if:

  • you puncture your skin with a used needle or other sharp object that has infected blood on it
  • someone with blood in their saliva bites you and breaks your skin

Lower risk of infection

The risk of an infection being passed on in someone else’s blood is lower if the blood comes into contact with your eyes, mouth, nose, or skin that’s already broken.

For example, if someone spits in your face, they may have blood in their saliva and it may get in your eyes, mouth or nose. The infected saliva may also get into an existing cut, graze or scratch.

There is also a lower risk of infection if infected blood comes into contact with skin that is already broken due to a health condition like eczema.

Very low risk of infection

The risk of infection is very low if infected blood comes into contact with unbroken skin.

Further information:

Page last reviewed: 17/03/2015

Next review due: 28/02/2018