SEPSIS claims five lives every hour in the UK - and more people die from it than breast, bowel and prostate cancer combined.
But why? Unfortunately it can be very hard to spot, often masking as a minor illness before spiralling into a killer condition.
From sweaty palms to a red rash and even diarrhoea , sepsis can present in various ways.
That's because it can affect many different areas of the body.
Dr Ron Daniels, founder and CEO of the UK Sepsis Trust , says: "Sepsis is a life-threatening condition arising when the body's response to infection causes organ damage."
This could be a urinary tract infection (UTI), pneumonia or even flu.
"It can lead to multi-organ failure and death, and for the majority of people, it develops in anywhere between 24 and 72 hours," Dr Daniels ad