Sweet's Syndrome in Dogs: Sterile Neutrophilic Dermatosis Explained

Based on peer reviewed veterinary research · For educational purposes only · Updated September 2026 · 8 min read

What Is Sweet's Syndrome in Dogs?

Sweet's syndrome, formally called acute febrile neutrophilic dermatosis, is a rare inflammatory skin disease in which dense collections of neutrophils infiltrate the skin without any infectious organism being present. Neutrophils are the white blood cells that normally fight bacteria, so in this condition the immune system is essentially attacking the skin without a microbial target.

The syndrome was first described in human patients by Robert Douglas Sweet in 1964 (Sweet, 1964). In dogs, comparable cases are reported infrequently and are usually grouped under the broader heading of sterile neutrophilic dermatoses, a category that also includes sterile neutrophilic pustulosis and related disorders described in veterinary dermatology references (Miller et al., 2013).

Because the disease is so uncommon, many veterinarians will consider it only after more likely causes such as bacterial pyoderma, drug reaction or autoimmune disease have been excluded.

What Causes a Sterile Neutrophilic Dermatosis?

The exact cause in dogs is not established. In people, Sweet's syndrome has been linked to infections, inflammatory bowel disease, certain medications and underlying malignancy. Veterinary sources suggest that a similar reactive mechanism, an exaggerated immune response triggered by another process, is likely in some dogs (Gross et al., 2005).

Possible triggers considered by clinicians include drug reactions, systemic inflammatory disease, and internal neoplasia. Our article on paraneoplastic skin syndromes in dogs explains how internal cancer can produce skin changes, and the guide to erythema multiforme and drug reactions covers medication-related eruptions.

In many cases no trigger is found, and the disease is labeled idiopathic (of unknown cause). This is why a thorough workup, not just skin treatment, is important.

How Do Veterinarians Diagnose Sweet's Syndrome?

Diagnosis is one of exclusion. The veterinarian begins with a full physical exam, complete blood count, chemistry panel and urinalysis, since fever and elevated white blood cell counts may accompany the skin lesions.

Skin cytology of a lesion shows numerous neutrophils but no bacteria, and the definitive step is a skin biopsy sent for histopathology plus bacterial and fungal culture of tissue. Our article on understanding dog skin biopsy results explains how to read a pathology report. Special stains help exclude deep bacterial, mycobacterial and fungal infection, which can mimic a sterile process.

Additional testing may be recommended to look for an underlying disease, such as imaging of the chest and abdomen. Autoimmune diseases are excluded with the help of tests such as those described in immunofluorescence testing for autoimmune dog skin disease. If you are trying to describe lesions before a visit, the Dog Skin Condition Checker can help.

Signs and Symptoms to Watch For

Reported signs include sudden onset of red, raised, painful plaques or nodules, sometimes with pustules, on the trunk, limbs, face or neck. Affected dogs may also have fever, lethargy, reduced appetite and joint or muscle discomfort.

The table below compares sterile neutrophilic disease with the look-alike conditions a veterinarian must exclude.

Treatment Options for Sweet's Syndrome

Treatment is prescribed and monitored by a veterinarian. Because the process is immune-mediated, therapy in the literature centers on immunosuppressive or anti-inflammatory medication, with the drug and dose chosen for the individual dog and any underlying disease (Miller et al., 2013). Related options are discussed in our articles on azathioprine for autoimmune skin disease and doxycycline for dog skin conditions.

Inflamed and broken skin is vulnerable to secondary infection. For that supportive role, Chlorhexidine Spray contains chlorhexidine gluconate, an antiseptic that disrupts bacterial cell membranes, together with ketoconazole, an azole antifungal that inhibits ergosterol synthesis in yeast. It is an FDA-registered OTC veterinary drug listed on DailyMed. It does not treat Sweet's syndrome or any immune-mediated process, and it should only be used on intact skin as directed by your veterinarian.

Do not stop or change prescribed medication without your veterinarian's guidance, since abrupt changes can lead to relapse.

Prevention and Long-Term Management

There is no proven way to prevent a rare idiopathic condition, but careful follow-up improves outcomes. Recheck visits allow the veterinarian to adjust medication, monitor bloodwork and watch for relapse, which is reported in people and should be anticipated in dogs.

Keep a record of medications, vaccines and supplements given before lesions appeared, as this helps identify drug triggers. Report new fever, lethargy or weight loss promptly, because these may point to an underlying illness. Gentle skin care, avoiding harsh scrubbing, and treating any secondary problems such as bacterial skin infections support recovery while the underlying disease is managed.

Frequently Asked Questions

What is Sweet's syndrome in dogs?

It is a rare, sterile inflammatory skin disease in which neutrophils fill the skin without infection. It was first described in people in 1964 and is only occasionally reported in dogs.

Is Sweet's syndrome contagious?

No. It is an immune-mediated condition, not an infection, so it cannot spread to other pets or people.

How do vets tell it apart from a bacterial skin infection?

They combine cytology, skin biopsy and tissue culture. A sterile dermatosis shows neutrophils with negative cultures and does not respond to antibiotics.

What causes it?

The cause is often unknown. In people it has been linked to infection, inflammatory bowel disease, drugs and cancer, so veterinarians look for underlying disease.

Sources

1. Sweet RD. An acute febrile neutrophilic dermatosis. British Journal of Dermatology. 1964;76:349-356.
2. Miller WH, Griffin CE, Campbell KL. Muller and Kirk's Small Animal Dermatology, 7th ed. Elsevier; 2013.
3. Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Skin Diseases of the Dog and Cat: Clinical and Histopathologic Diagnosis, 2nd ed. Blackwell Science; 2005.
4. Hnilica KA, Patterson AP. Small Animal Dermatology: A Color Atlas and Therapeutic Guide, 4th ed. Elsevier; 2017.

Related Reading

• Pemphigus in Dogs: Autoimmune Blistering Disease
• Dog Skin Biopsy Results: What They Mean
• Azathioprine for Dogs: Managing Severe Autoimmune Skin Disease

E. Maddens

Founder of Vetified. Develops topical antifungal and antimicrobial formulations for companion animals. Vetified products are listed on DailyMed and manufactured through FDA-registered facilities in the United States.

Research basis: All Vetified content references peer reviewed research published in journals including Veterinary Dermatology, JAVMA, and Journal of Small Animal Practice.