Quick answer
An infection is an illness caused by germs getting into the body. An injection is medicine put into the body with a needle. An ear infection; a flu injection. An injection can treat or prevent an infection, which is how the two end up in the same sentence.
The core difference
- infection — disease caused by bacteria, viruses or other organisms entering the body. A chest infection, the wound became infected, infection control.
- injection — the act of putting a liquid into the body with a syringe, or the dose itself. A tetanus injection, by injection, an insulin injection.
The tell
Infection belongs with infect and infectious — something gets in and spreads. Injection belongs with inject and syringe — something is put in on purpose. The f and the j are the only difference on the page; the needle is the difference in the room.
In use
- infection — The cut developed an infection. Wash your hands to limit the spread of infection.
- injection — The nurse gave the injection in the upper arm. Some vaccines are given by injection, others by mouth.
Common slips
- an ear injection → an ear infection
- the flu infection (meaning the shot) → the flu injection
Infection gets in; injection is put in.
Where the words come from
Infection is from Latin inficere, "to stain, to taint" (in- + facere "to make"). Injection is from Latin inicere, "to throw in" (in- + iacere "to throw") — the same ject as eject and project.
Frequently asked questions
Can an injection cause an infection?
Any break in the skin can, which is why injections are given with sterile needles. The words still mean different things.
What is an infectious disease?
One that can be passed from person to person. Infectious is the adjective from infection.
Is "jab" the same as injection?
In British English, yes — informal for an injection, especially a vaccination. Questions about any injection or infection belong to a doctor or nurse.
