Eosinophils are a type of white blood cell involved in allergic reactions. In dogs they can build up in the skin and mouth and cause two main problems: eosinophilic furunculosis, a sudden, painful inflammation of the hair follicles that mostly affects the face, and eosinophilic granulomas, which are rare in dogs and usually found in the mouth [1][2][4]. Both are thought to be overreactions of the immune system, and insect or spider bites are among the suspected triggers for the facial form [2][4].
If your dog’s face swells suddenly, or your dog has trouble breathing, see a vet now. Do not try home remedies first. Sudden facial swelling has several possible causes, some of them emergencies; see our post on hives and facial swelling in dogs.
In cats, eosinophilic lesions are much more common and are covered in our post on eosinophilic granuloma complex in cats.
Eosinophilic furunculosis of the face
A 2025 case report summed up the condition in dogs this way: it comes on very quickly, with painful sores and crusts on the ears, lips or around the eyes, and suspected causes include bites from insects or spiders, as well as some worms [2]. Stings are common on the face: in a 2024 study of 178 dogs treated for bee or wasp stings at a Swiss university hospital, the face was the most common sting site (39% of dogs where the site was recorded), followed by the paw and the inside of the mouth. Dogs stung inside the mouth were more likely to have a severe whole-body reaction [5].
What you may notice [1][2]:
- Lesions that appear over hours to days and may be painful or itchy.
- Red, raised bumps and pus-filled spots on the top of the muzzle.
- Open sores and crusts on the lips, around the eyes or on the ears.
- In some dogs, spots spread beyond the face.
In a 1995 report of three dogs, the bumps and sores appeared quickly on the top of the muzzle. Two dogs had lesions only on the face, and the third had pus-filled spots over more of the body. The authors noted that similar facial cases had earlier been called “nasal pyoderma” (a bacterial infection of the nose) [1]. Sudden swelling on the nose after an insect sting is also mentioned in our post on dry, crusty nose in dogs.
Eosinophilic granulomas
Eosinophilic granulomas are uncommon in dogs and poorly understood. They usually show up in the mouth as a raised mass, a flat plaque or an ulcer [4]. The way the lesions look under the microscope, where they appear and how they respond to anti-inflammatory treatment all point to an allergic-type reaction, although the exact cause is not known [4].
- Mouth lesions in 24 dogs: a 2019 review of 17 years of records from a veterinary teaching hospital and a private referral practice found most lesions on the palate (65.4%), then the tongue (26.9%), with the rest elsewhere in the mouth (7.7%). The dogs came from 15 breeds; Cavalier King Charles Spaniels made up 16.7%, and Labrador Retrievers and West Highland White Terriers 12.5% each. Smaller dogs were more likely to have lesions on the palate or tongue, and larger dogs on the lips or cheek lining [3].
- Signs in three Cavalier King Charles Spaniels: a 1996 report from Norway described dogs that kept clearing their throats, had trouble swallowing, coughed while or after eating, ate less and found eating difficult [4].
How it is diagnosed
- Eosinophilic furunculosis: in the 1995 report, skin biopsies showed large numbers of eosinophils clustered around the hair follicles [1]. Your vet may also look at cells from the lesion under the microscope.
- Eosinophilic granulomas: in the 1996 report, collecting cells from the lesion was simpler than a biopsy because the tissue was fragile, but it was not enough to confirm the diagnosis. A tissue biopsy confirmed it in every dog [4].
- Looking for a trigger: when lesions return, your vet may look for insect exposure or an underlying allergy [2][4].
Treatment
Treatment is chosen by your vet. The studies give a general picture:
- Furunculosis: in the 1995 report, the three dogs did not get better on antibiotics alone but improved quickly once a steroid was added, and the authors suggested steroids are useful for this condition [1]. Fast-acting anti-inflammatory treatment is usually needed because the lesions are painful [2].
- Mouth lesions: the authors of the 2019 study suggested that dogs with mouth lesions but no signs of illness may do well with a cautious, step-by-step approach [3].
Do not give your dog human allergy or pain medicines for a swollen face unless your vet tells you to.
Outlook
Outcomes vary between studies:
- In the 1995 report, all three dogs with facial furunculosis responded quickly once anti-inflammatory treatment was added [1].
- In the 2019 study of mouth lesions, every dog with a lesion on the palate had no signs at its last recheck; the median follow-up was 5 months [3].
- In the 1996 report of three Cavalier King Charles Spaniels, the response to steroid treatment ranged from full recovery to no visible change, so the authors judged the outlook to be uncertain [4].
These are figures and statements about groups of dogs in particular studies. They do not prove that a treatment caused an outcome, and they cannot predict how one dog will do. Your vet can explain what the findings mean for your dog.
When to see your vet
See a vet now if your dog has sudden facial swelling or trouble breathing.
See your vet if your dog has:
- swollen, red or painful bumps on the muzzle, lips, ears or around the eyes [1][2]
- bumps, plaques or sores in the mouth or on the lips [3][4]
- clearing of the throat, coughing during or after meals, trouble swallowing or eating, or reduced appetite [4]
- sores that become open or crusted [2]
- lesions that come back after treatment
FAQ
Can a bee sting cause this?
Insect and spider bites are among the suspected triggers of eosinophilic furunculosis in dogs [2], and the face is where dogs are most often stung [5]. Any sudden facial swelling needs a vet.
Is it the same as the eosinophilic granuloma complex in cats?
The conditions are related, but eosinophilic skin disease is much more common in cats than in dogs [2][4]. See our cat post.
Which dogs get mouth granulomas?
Many breeds can be affected. Cavalier King Charles Spaniels appear often in published reports [3][4].
Can it come back?
Yes. Lesions can return, and when they do your vet may look for an allergy or insect exposure behind them [2][4].
The bottom line
Eosinophilic furunculosis causes sudden, often painful bumps and sores, most often on the muzzle, and insect or spider bites are among the suspected triggers [1][2]. Eosinophilic granulomas are rare in dogs, usually appear in the mouth and are thought to be an allergic-type reaction [3][4]. If your dog’s face swells suddenly or your dog has trouble breathing, see a vet now.
This article is for general information and does not replace a visit to your veterinarian. If your dog’s face swells or your dog has a sore in the mouth, contact your vet.
Sources
- Curtis CF, Bond R, Blunden AS, Thomson DG, McNeil PE, Whitbread TW. Canine eosinophilic folliculitis and furunculosis in three cases. J Small Anim Pract. 1995;36(3):119-123. https://pubmed.ncbi.nlm.nih.gov/7783436/
- Ehling S, Marx AH, Busse C, Beineke A, Volk AV. Oclacitinib Treatment and Surgical Management in a Case of Periocular Eosinophilic Furunculosis and Vasculitis with Secondary Eyelid Fusion in a Diabetic Cat. Vet Sci. 2025;12(6):589. Open access (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC12197539/
- Mendelsohn D, Lewis JR, Scott KI, Brown DC, Reiter AM. Clinicopathological Features, Risk Factors and Predispositions, and Response to Treatment of Eosinophilic Oral Disease in 24 Dogs (2000-2016). J Vet Dent. 2019;36(1):25-31. https://pubmed.ncbi.nlm.nih.gov/31138045/
- Bredal WP, Gunnes G, Vollset I, Ulstein TL. Oral eosinophilic granuloma in three cavalier King Charles spaniels. J Small Anim Pract. 1996;37(10):499-504. https://pubmed.ncbi.nlm.nih.gov/8912245/
- Chapman E, West EA, Kosnik M, Fischer NM, Favrot C, Beeler L, Rostaher A. Natural History and Risk Factors of Hymenoptera Venom Allergy in Dogs. Animals (Basel). 2024;14(22):3220. Open access (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC11591281/