The exact cause is not fully understood, but it involves an overactive immune response, particularly involving neutrophils.

In simple terms, the immune system becomes overactivated and doesn’t switch off properly, leading to inflammation in the skin and sometimes other parts of the body.

Common triggers

Sweet syndrome is often triggered by:

• Infections (especially respiratory or gastrointestinal)
• Certain medications (e.g. some antibiotics, G-CSF)
• Autoimmune or inflammatory diseases
• Pregnancy
• Cancer (especially blood cancers such as leukaemia)

Some people have genetic markers (e.g. HLA-B54), but this does not mean they will develop the condition.

Symptoms usually develop quickly (over days) and may include:

Skin changes

• Painful red, purple, or raised lesions
• May look like bumps, plaques, or nodules
• Often appear on the face, neck, and arms, but can occur anywhere

General symptoms

• Fever (often above 38°C)
• Fatigue and feeling unwell
• Joint pain
• Eye inflammation (e.g. redness, irritation)

The rash can appear quite dramatic and may be mistaken for infection or other skin conditions.

There is no single definitive test. Diagnosis is made using a combination of:

• Clinical features (typical rash + fever)
• Blood tests (showing inflammation and increased neutrophils)
• Skin biopsy, which confirms the diagnosis by showing neutrophil infiltration without blood vessel inflammation

Doctors will also rule out other conditions that can look similar, such as:

• Vasculitis
• Erythema nodosum
• Panniculitis
• Other inflammatory syndromes

Simplified diagnostic criteria

Doctors typically look for:

Key features:

• Sudden painful rash
• Characteristic biopsy findings
• Plus supporting features (at least two):
  • Fever
  • Recent trigger (infection, cancer, etc.)
  • Abnormal blood tests (inflammation)
  • Rapid response to steroids

Is it autoimmune or autoinflammatory?

Sweet syndrome is considered autoinflammatory, meaning it involves the body’s early (innate) immune system.

However, the boundaries between immune conditions are not always clear, and ongoing research continues to explore this.

The main treatment is corticosteroids, which usually work quickly and effectively.

Other treatments (if needed) include:

• Colchicine
• Non-steroidal anti-inflammatory drugs (NSAIDs)
• Targeted therapies (e.g. anakinra, anti-TNF agents)

Most people improve within days to weeks, although complete resolution may take longer.

During active episodes, symptoms can be:

• Physically uncomfortable
• Visually noticeable
• Emotionally distressing

It’s important to:

• Seek early medical care
• Follow treatment plans
• Address both physical and emotional wellbeing

With appropriate care, most people recover well and return to normal life.

What is the outlook?

• Most patients respond very well to treatment
• Symptoms can be painful and disruptive, especially during flare-ups
• The condition can sometimes come back (relapse)
• A small number of patients develop chronic or recurring disease

Because Sweet syndrome can sometimes be linked to underlying conditions (especially cancers), doctors may recommend further investigations depending on the situation.