Sepsis is a life-threatening condition that can develop rapidly and without warning. It happens when the body’s immune system overreacts to an underlying infection, triggering widespread inflammation that can lead to organ dysfunction, septic shock, and - if the condition is not recognised and treated quickly - death. Identifying red flag sepsis symptoms early gives doctors a critical window to act before the condition becomes harder to manage.

In clinical practice, healthcare providers use red flag sepsis criteria to assess people who appear acutely unwell. These are often used alongside screening tools and established therapeutic pathways to help identify patients presenting with suspected sepsis. If there is any clinical suspicion, the priority is always to start early management as quickly as possible, often within one hour.

In this guide, we explain what kind of symptoms may be a red flag for sepsis, when you should take urgent action, and what kind of treatment needs to be provided. We will also examine what can happen if treatment is delayed or missed entirely, and what you should do if you find yourself or a loved one in this position.

What Is Sepsis?

Sepsis happens when the body’s immune system overreacts to an infection, and is closely related to systemic inflammatory response syndrome. Instead of staying focused on one area, the response spreads through the bloodstream, causing widespread inflammation that can quickly damage organs. Doctors treat sepsis as a life-threatening emergency because a seemingly mild infection can turn into red flag sepsis within hours.

The following groups are considered to be at highest risk of developing sepsis:

• Babies and young children, as their immune systems are still developing.
• Adults over 65, as natural immunity weakens with age and long-term illnesses are more common.
• People with weakened immune systems, including anyone taking long-term steroids, chemotherapy, or other immune-suppressing medicines.
• Anyone with a serious wound or existing infection, such as pneumonia, a urinary tract infection, or an infection after surgery.
• Pregnant women and new mothers, because pregnancy alters how the body responds to infection.

Although sepsis can affect anyone, these groups face a higher chance of moving rapidly from infection to severe, red flag symptoms that demand urgent hospital care.

For a deeper explanation of how sepsis progresses, see our guide to the three stages of sepsis. You can also find medical guidance on the NHS sepsis page.

What Other Sepsis Symptoms Should You Be Aware Of?

In addition to these sepsis red flag symptoms, there are a number of other signs that could potentially indicate a case of sepsis:

• Feeling extremely unwell or that something is seriously wrong
• Not passing urine all day (for adults and older children) or in the last 12 hours (for babies and young children)
• Vomiting repeatedly or being unable to keep down any fluids or food (for babies and young children)
• Swelling, redness, or pain around a cut or wound
• A very high or very low temperature
• Chills and shivering

If these symptoms develop or worsen quickly, especially after an infection or illness, seek urgent advice by calling NHS 111. Early assessment and intervention can prevent progression to severe sepsis.

For more guidance, visit the NHS sepsis page.

How Does Sepsis Need to Be Treated?

Sepsis is a medical emergency, and treatment must start quickly to prevent serious health complications. If doctors identify red flag sepsis symptoms, immediate hospitalisation and rapid treatment are essential. Early recognition and prompt intervention can greatly reduce the risk of severe outcomes like septic shock, acute respiratory distress syndrome (ARDS), organ dysfunction, and even death.

Once the specific type of bacteria causing the infection is identified, treatment can be provided depending on the severity of the condition and the underlying cause. Options may include:

• 24-hour treatment in an intensive care unit
• Intravenous fluids to maintain blood pressure and prevent organ damage
• Medication to raise blood pressure and prevent septic shock
• Oxygen therapy to provide adequate oxygen supply to organs and tissues
• Corticosteroids to reduce inflammation
• Medication to alleviate pain, fever and other symptoms
• Surgery to remove the source of the infection

The Sepsis Six

In UK hospitals, healthcare providers use a recognised set of medical actions known as the Sepsis Six. Doctors and nurses should deliver these treatments within one hour of identifying red flag symptoms or strongly suspecting sepsis. Quick intervention improves patient survival and reduces long-term complications.

The Sepsis Six includes:

1. Giving oxygen
   Providing high-flow oxygen helps keep oxygen levels stable, ensuring vital organs receive the oxygen they need to function properly.
2. Taking blood cultures
   Blood samples are taken immediately to identify which bacteria or other pathogens are causing the infection. Identifying the infection helps doctors choose the most effective antibiotics.
3. Administering intravenous antibiotics
   Strong antibiotics are given directly into the bloodstream. Doctors do this urgently, usually without waiting for blood culture results, due to the importance of rapid action. The antibiotics chosen initially are broad-spectrum, meaning they target a wide range of possible infections, and can later be adjusted based on test results.
4. Administering intravenous fluids
   Intravenous fluids help maintain blood pressure and circulation, ensuring oxygen and nutrients continue reaching vital organs. This reduces the risk of septic shock, a condition where blood pressure drops dangerously low.
5. Measuring lactate levels
   A blood test for lactate indicates if the patient’s organs are getting enough oxygen. Higher lactate levels suggest organs may be struggling or failing due to insufficient blood flow.
6. Monitoring urine output
   Doctors closely monitor urine output, as reduced or absent urine can indicate kidney problems and poor circulation. This helps healthcare teams quickly identify if treatment needs adjustment.

The Sepsis Six framework was developed by the UK Sepsis Trust. These interventions are supported by clear clinical guidelines, including those from the National Institute for Health and Care Excellence (NICE). Early recognition of red flag sepsis symptoms and starting the Sepsis Six promptly significantly improves outcomes for most patients.

How Long Do You Have to Administer the Sepsis Six in a Red Flag Sepsis Case?

In cases where red flag sepsis symptoms are spotted, healthcare providers must deliver the Sepsis Six treatments within one hour of identifying severe symptoms. This critical time window is often referred to by doctors and nurses as the "golden hour" because rapid treatment can dramatically improve a patient's chances of survival.

The urgency behind this timeframe is based on clear medical evidence. Studies show that the longer sepsis goes untreated, the higher the risk of severe complications.

Each minute counts. Delays in starting antibiotics, fluids, or oxygen - even by an hour or two - can significantly increase the risk of serious long-term health issues or mortality. Because of this, clinical guidelines from NICE and the UK Sepsis Trust emphasise the importance of healthcare teams acting quickly when patients present with red flag sepsis symptoms.

Rapid identification using clinical tools, such as the National Early Warning Score, combined with clear red flag sepsis criteria, ensures the Sepsis Six bundle starts promptly, maximising the likelihood of recovery and reducing the chance of complications.