Infection vs Sepsis

When to use each in English, with meaning, register, and examples.

Infection

Top 1,000 (very common) B2 noun

Sepsis

Formal Beyond 10,000 (less common)

Most formal: Sepsis Most common: Infection

	Infection	Sepsis
Pronunciation	🇬🇧 /["/ɪnˈfekʃn/"]/ 🇺🇸 /["/ɪnˈfekʃn/"]/	🇬🇧 //ˈsɛpsɪs// 🇺🇸 //ˈsɛpsɪs//
Meaning	When germs or bacteria get into the body and make you sick.	A serious infection affecting the whole body.
Example	The doctor confirmed that the patient had a bacterial infection in his lungs.	The patient was diagnosed with sepsis after showing signs of severe infection.
Register	Neutral	Formal
How common	Top 1,000 (very common)	Beyond 10,000 (less common)
CEFR level	B2	-
Part of speech	noun
Collocations	nasty, serious, severe, have, suffer, suffer from, develop, occur, spread, in infection, infection from, infection through, a cause of infection, the onset of infection, resistance to infection, nasty, serious, severe, have, suffer, suffer from, develop, occur, spread, in infection, infection from, infection through, a cause of infection, the onset of infection, resistance to infection	diagnose sepsis, treat sepsis, sepsis symptoms, severe sepsis, septic shock
Antonyms	health, wellness	-
Common mistakes	Confused with 'inflection' (change in speech), Using 'infection' to refer to non-medical situations, Incorrectly stating a person is an 'infection' instead of having an 'infection'	Confused with 'septic' which refers to infection but not specifically a systemic condition., Used in casual contexts, which may trivialize its seriousness., Misunderstood as a common illness instead of a critical condition.
Usage notes	Use 'infection' in medical or health contexts. It's appropriate for conversations with healthcare professionals or when discussing illnesses. Avoid using it in casual or non-serious discussions.	Used mainly in medical contexts. Not common in everyday conversation. Important in healthcare discussions and emergencies.

See it in real clips

They attack, like white blood cells fighting an infection.

The Pitt › S1 E1

Good pulse and blood pressure. No signs of infection.

They attack, like white blood cells fighting an infection.

The Pitt › S1 E1

Good pulse and blood pressure. No signs of infection.

Infection

Frequently asked questions: Infection vs Sepsis

What's the difference between Infection and Sepsis?

Infection: When germs or bacteria get into the body and make you sick. Sepsis: A serious infection affecting the whole body.

Which is more formal: Infection and Sepsis?

Sepsis is the most formal of these.

Which is more common: Infection and Sepsis?

Infection is the most common in everyday English.

Can you show an example of each?

Infection: The doctor confirmed that the patient had a bacterial infection in his lungs. Sepsis: The patient was diagnosed with sepsis after showing signs of severe infection.

Can I use Infection and Sepsis interchangeably?

Not always. Infection and Sepsis are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.