Furunculosis in Dogs – How to Help

Furunculosis is a bacterial infection of the deeper layers of the skin in dogs and cats.

These infections usually occur after something else causes the skin to become irritated, allowing bacteria to set up shop and grow out of control in parts of the body. When this happens, pets can develop red, tender bumps on their skin that can break open and drain fluid, or sometimes they can develop painful areas of swelling and redness with crusting and open sores.

Furunculosis is not something you can treat without a veterinarian’s help – some types of furunculosis can be very dangerous and make your pet very sick, so seeing a veterinarian as soon as possible is important if you think your dog has an infection.

In this article, we’ll talk about several types of deep tissue inflammation and infections, but it’s always important to remember that the skin damage or irritation comes first and the infection second! Your veterinarian will want to treat the infection and also discuss ways to control the underlying cause of the inflammation, so this doesn’t happen again.

Post-Grooming Furunculosis

Cause

Post-grooming furunculosis is one of the simplest, but also the most dangerous types of furunculosis.

It occurs, as the name suggests, after your dog has a bath. When the skin is wet, rubbing or scrubbing too hard at the haircoat can cause the skin to become irritated and less able to defend itself against infection. This can occur if you scrub aggressively back and forth while lathering shampoo or brush your dog while they’re being bathed.

After the skin is irritated, it can become contaminated by shampoo or water that contains infectious bacteria. The most common cause of post-grooming furunculosis is Pseudomonas aeruginosa, a rod-shaped bacteria that is not found on the skin normally – it's most commonly found in water or soil.

Appearance

The lesions in dogs with post-grooming furunculosis are usually on the back from the shoulders to the rump, which are the areas where people tend to scrub the most vigorously during bathing. They can occur around 1 – 2 days after a bath.

Dogs develop red, raised bumps that can break open and drain (you may see clear, pink liquid), and they can be very painful and itchy in the affected areas. Additionally, dogs can become systemically very sick with fevers, inflamed lymph nodes, vomiting, weakness, and diarrhea in some cases.

Often, the first signs you’ll notice at home are your dog scratching or rubbing their back constantly, seeming painful when you touch the itchy areas, and suddenly being more tired and less interested in playing or going on walks. 

Treatment

The most important part of treating post-grooming furunculosis is antibiotics. Your veterinarian will take a surface sample to look under the microscope for bacteria. If they find some, they’ll take a culture sample to find out what type of bacteria is present and what antibiotic can be used to treat it. They may also take small punch samples (about the size of a pencil eraser) of your dog’s skin for a biopsy to make sure they’re treating the right condition.

Since dogs are often very sick when they develop post-grooming furunculosis, many veterinarians will prescribe an antibiotic that usually works against Pseudomonas bacteria immediately, then change it if the culture results say something else will work better. Dogs often need antibiotics for 3 to 4 weeks at least, and sometimes longer if the infection is very deep in their skin.

If your pet is in pain, your veterinarian may prescribe pain medications to make them more comfortable. If your dog is very sick, they may need to stay at the hospital for a few days for additional fluid administration intravenously (IV – in their veins) and other supportive treatments to get them back on their feet as soon as possible.

Prevention

Since post-grooming furunculosis is a very scary disease, preventing it is crucial! The most important way to prevent this is to avoid scrubbing or brushing your dog during baths. Gently massaging their skin and hair in the direction you’d pet them is the least irritating way to bathe your dog. Using a silicone versus a wire or bristle brush is also advised. We like the Furbliss brush.

SHAMPOO DILUTION PRO TIP: Studies have shown that Pseudomonas bacteria easily grow in diluted shampoo bottles, so don’t keep bottles of diluted shampoo around. If you want to dilute your dog’s shampoo during baths, place a small amount of undiluted shampoo in a cupped palm, then gently add water to it and mix between your hands to dilute it and form a lather. Keeping your dog’s shampoo bottle out of the shower will also prevent water from getting in around the cap and accidentally diluting your shampoo.

Interdigital Furunculosis

Cause

Interdigital furunculosis or interdigital cysts (abscesses between the toes) are small red bumps and swellings that can occur between your dog’s toes on the tops and bottoms of their feet. These bumps have many possible causes, including food allergies, environmental allergies (such as pollens or dust mites), short-coated dog hairs causing irritation, abnormal weight distribution on the parts of the foot when standing, foreign material (like small grass seeds or foxtails) penetrating the skin, and some parasites like Demodex mites.

A bacterial infection often develops after the initial inflammatory trigger. It is rare that dogs develop only one episode of furunculosis in their lifetime unless it is due to foreign material, so your veterinarian will want to look for why this keeps happening to make sure they can prevent it in the future.

Appearance

The red bumps or cysts between your dog’s toes more often affect the front feet, but they can affect all four feet in some dogs. They can break open or become ulcerated on their surface to form draining tracts, and the furunculosis can cause irritation to surrounding tissues that make them red and swollen.

Many pets are painful or itchy on their affected feet, which often leads to dogs licking their swollen paw and limping. As the nodules heal, they can scar and be more likely to recur when inflammation is triggered in the future. This is especially common in pets with chronic interdigital cysts, so catching and treating these nodules early is important for your pet’s quality of life in the future.

Treatment

The nodules themselves are often infected and can require antibiotics for at least 3–4 weeks, sometimes longer, so your veterinarian will check a sample of the surface or the draining fluid under the microscope to look for bacteria.

If your dog has had infections in the past, they may also take a culture swab of the nodule to find out the best antibiotic to use to treat your pet.

Your dog may benefit from 5–10 minute Epsom salt foot soaks to reduce inflammation, and your veterinarian may prescribe oral steroids for a few weeks to decrease swelling.

There are newer treatments available now, like a Phovia® light, which is a special LED light that is combined with a light-activated gel in weekly treatments to produce wavelengths that kill bacteria, reduce inflammation, and help nodules like this heal faster. Your veterinarian will recommend using this if they feel it will be helpful in your dog’s case. It is rare that your dog will need surgery to remove a nodule, but it may be necessary when a lesion is chronic and has a lot of scar tissue.

Prevention

After the nodule itself heals, your veterinarian will want to focus on making sure it doesn’t come back. If your veterinarian suspects your dog could have an allergy, they may discuss a diet trial with you, environmental allergy testing, or potentially oral allergy control medications to reduce your pet’s symptoms.

If your vet suspects your pet is putting pressure on their feet incorrectly (like when a person stands with their feet turned too far out or in), they may want to discuss physical therapy or other measures to help correct this.

Sometimes, especially in dogs like English Bulldogs, their short hairs can cause enough irritation in their skin to trigger nodules to develop. In those cases, your veterinarian may recommend regular paw wipes and anti-inflammatory drops on your pet’s feet to minimize this skin irritation. A lot of the time, dogs can have more than one problem at once, like English Bulldogs that have short hair issues and allergies. This means that your veterinarian will have to use a combination of treatment options to keep your dog’s paws as comfortable as possible.

Lick Granuloma

Cause

Lick granulomas are sometimes infected and sometimes not, so they don’t fit neatly into the furunculosis category.

They are caused by a dog constantly, obsessively licking one particular area long enough that it forms layers of scar tissue and inflammation, and often becomes infected through overgrowth of a pet’s own skin bacteria as a result of the inflammation.

The most common causes of dogs licking like this are itching from allergies, pain from injuries or arthritis, skin parasites like Demodex mites, or behavioral problems like anxiety or boredom.

Appearance

Lick granulomas appear as thickened, hairless patches on the body with well-defined borders. The skin is often red and raised, and it sometimes has crusting and open sores especially if the granuloma is infected.

Your pet may have brown staining in the hair around the lick granuloma, or the hair can appear matted from the constant moisture. Most often, they appear on the front legs, but anywhere your dog can reach to lick could be affected.

Treatment

Identifying the cause of the lick granuloma and breaking your dog’s compulsion to lick the area are crucial parts of treating this problem. Your veterinarian may want to have your dog wear an Elizabethan collar (plastic cone or 'donut') to keep them from licking the area, and may also prescribe pain medications or anti-itch treatments to make your dog more comfortable.

If the lick granuloma is infected, your veterinarian may prescribe oral or topical antibiotics and may collect a culture from the skin to determine what antibiotic is best.

Weekly Phovia® light treatment at your dog’s veterinary clinic can also help the area heal faster and decrease skin inflammation and infection.

It usually takes weeks to months for a lick granuloma to develop, so it will take a similar amount of time for it to resolve. Your pet will hopefully start to feel better quickly, but it takes patience and diligent treatment from you and your vet to heal a lick granuloma completely.

To look for why this is happening, your veterinarian may take X-rays of the bones under your dog’s lick granuloma to check for arthritis, small fractures or breaks, or signs of misalignment.

They may want to discuss allergy management if they suspect your dog is itchy due to allergies, and your veterinarian may check for parasites, like Demodex mites, that can cause inflammation.

If they do not find anything with these tests, they may discuss environmental enrichment to reduce boredom and anxiety management through medications or training.

Prevention

The key to prevention is identifying why your dog developed a lick granuloma and treating it. Once your veterinarian identifies the cause, being consistent with your pet’s prescribed treatments is the most important thing.

In the future, your pet could develop new lick granulomas if their condition is not identified or if it can’t be completely controlled. If you notice your pet starting to bother a particular area, quickly stop them from bothering it using an Elizabethan collar or donut, and call your veterinarian to be seen as soon as possible. Stopping a lick granuloma before it becomes chronic will make it much easier to treat.

Perianal Fistulas

Cause

Perianal fistulas are sometimes called anal furunculosis, but this isn’t the correct term. Often, dogs with perianal fistulas don’t have a skin infection at all!

We’ll talk about them here because they are a type of deep inflammation, but any skin infection that occurs, like with lick granulomas, is very much secondary to the underlying condition, and treating the infection won’t make the condition itself go away.

Perianal fistulas are a chronic inflammatory condition that occurs in German Shepherd dogs especially, though it can affect other breeds. It’s not completely known why this condition occurs, but it appears to have an immune-mediated inflammatory component, may involve food allergies in some dogs, and could be genetically predisposed in German Shepherds.

Appearance

Perianal fistulas appear as small, draining holes (called draining tracts) around the outside of the anus. Usually only one or two are present at once, but some pets can have more. The draining tracts do not run into the anus itself but instead involve the skin around it.

These tracts produce discharge that looks like pus because of the inflammatory cells involved in this condition, but it can sometimes look more like clear, bloody liquid around their anus.

Dogs often lick this area constantly due to irritation. Bacterial infections can develop easily because the open wounds are right next to the anus. The skin can be swollen, tender to the touch, and crusted (especially if there is an infection involved), and your dog may not want anyone to go near the area because it hurts. They may also be reluctant to defecate or be painful when they poop because of this swelling.

Treatment

If your veterinarian suspects your dog has perianal fistulas, they’ll want to check for infection under the microscope and treat it with oral antibiotics if one is present.

They may also recommend a diet trial to find out if part of the problem for your pet is a food allergy.

Your dog will likely need lifelong medication to control their perianal fistulas, and this usually involves a type of drug called a calcineurin inhibitor. This type of drug is immune suppressive and reduces the unnecessary inflammation from your dog’s immune system that is triggering the fistulas to appear. There is a topical version, called tacrolimus, and an oral version, called modified cyclosporine. Sometimes pets require both, but since these medications require a prescription, your vet will be able to recommend what should work best for your pet.

Prevention

Unfortunately, there isn’t a way to prevent perianal fistulas from happening in the first place. However, if your dog has already been diagnosed with this condition and you notice that they are starting to lick their anus again, bring them to your veterinarian to have the area rechecked. That way, if your dog’s condition starts to flare up, you can get on top of treating it quickly, try to prevent an infection from developing, and help it heal more easily.

In summary, there are a lot of different kinds of conditions that are referred to as furunculosis. It is important to remember that infections are always secondary to the underlying cause of the skin inflammation, so working with your veterinarian to find, treat, and prevent that cause is crucial to helping your dog feel their best.