Causes of skin allergies and skin infections in dogs

Seasonal allergy versus food allergy in dogs

The two most common causes for skin itching and infection in dogs are seasonal allergies (environmental allergy) and food allergies.  Just like there are a lot of people that suffer from allergies, there are a LOT of dogs who suffer from allergies too.  While human allergies show up as nasal congestion and sneezing, your dog’s most common allergy symptoms are itchy skin, hair loss and skin/ear infections.

If you’re looking for an over the counter product to combat your dog’s regular bouts of itching, skin infections, dandruff and dry coat, try Dermoscent’s Essential 6 fatty Acid Pipettes. These are pipettes that you apply to your dog’s skin weekly for 2 months. They are available on Amazon and have rave reviews.

If your dog is having these symptoms, how do you know what they are reacting to? 

A lot of people assume that food is the culprit for their dog’s itchy skin and hair loss. However, food allergy occurs in less than 5% of dogs and cats with skin disease and accounts for only 10-25% of pets with allergic skin disease.  However, dogs with seasonal allergies are at higher risk for ALSO developing food allergies. 

The age of onset of skin symptoms /reactions is a big clue to diagnosing food allergy versus seasonal allergy.  Food allergies in dogs typically develop in dogs before 1 year of age or after 7 years of age.  These two time points in a dog’s life are when there are increases in gut permeability. This “ leaky gut” causes proteins to leak from the GI tract and the immune system may then react to these proteins as foreign.

Food allergy triggers in dogs

Although a food allergy can develop to any food, the most common foods that trigger allergy are proteins and less commonly grain. 

Common food allergen triggers: 

• Beef
• Dairy
• Chicken 
• Lamb
• Wheat

Less common food allergy triggers

• Soy
• Corn
• Egg
• Pork 
• Fish
• Rice

Food allergy signs

Common breeds of dogs with food allergy: 

• Soft coated wheaten terrier
• Dalmatian
• West Highland white terrier
• Collie
• Shar-pei
• Lhasa apso
• Cocker spaniel
• Springer spaniel
• Miniature schnauzer
• Labrador retriever
• Dachshund
• Poodle
• German Shepherd
• Golden retriever
• boxer

Food elimination trial in dogs

The gold standard to diagnose food allergies is with a food elimination trial.  While blood testing to diagnose food allergies is standardly used in human medicine, it has not been shown to produce consistently reliable results in dogs and cats.

Seventy-five percent of food allergic dogs react to:  beef, dairy, chicken, wheat and lamb.  

A food elimination trial uses a food whose protein is highly digestible (>87%) or proteins that are already hydrolyzed, contains only 1 or 2 novel protein sources (novel proteins are proteins your dog has not eaten before), is free of additives, has low levels of vasoactive amines (like histamine) and is nutritionally adequate for the pet’s species, age and lifestyle.  ( Examples of food high in vasoactive amines are bananas, nuts, spinach and tomatoes). 

Most of the food allergens that trigger symptoms in dogs are between 10 to 70kDa.  And are able to link to IgE to produce skin reactions. 

Veterinary prescription foods are either hydrolyzed or novel-protein based. 

 Special hydrolyzed diets contain proteins and carbohydrates that are broken down into very tiny pieces that are below the size capable of producing reactions. 

The other prescription foods for food allergy offer “novel proteins” meaning protein sources that your dog has not already been exposed to such as lamb, venison, rabbit and even kangaroo.

An elimination diet trial should continue for at least 8 to 10 weeks.  During this time, your dog would be fed exclusively a hypoallergenic diet (either a prescription hydrolyzed diet or a novel protein diet). 

Food allergy symptoms and food allergy diet

When moving onto an elimination or hydrolyzed  diet, gastrointestinal symptoms typically improve within 2-3 weeks.  Skin signs take longer to improve: on average 4-12 weeks. 

By 5 weeks, 80% of patients have their skin signs go into remission and 90% by 8 weeks.  

Examples of food allergy veterinary diets: 

Hydrolyzed protein veterinary diets

• Hills Z/D  diet : contains chicken
• Purina HA diet: contains chicken or soy
• Royal canin HP diet: contains chicken
• Royal canin ultamino diet: conhttps://amzn.to/3iQDVnxtains chicken by products (chicken feather protein)

Novel protein veterinary diets
 

• Hills d/d diet: venison, salmon or duck
• Royal canin select  PR diet:  contains: potato, rabbit, hydrolyzed soy

Home prepared food allergy diets for dogs

It is possible to provide a home-prepared hypoallergenic diet, but these diets can be labor intensive and challenging to create a palatable diet which meets your dog’s nutritional requirements.  Home cooked diets are preferably made with one novel protein and one carbohydrate source. A novel protein is a protein your dog has not been exposed to in the past.  Preferably, the protein should also not be related to previous proteins your dog has consumed. For example if your dog ate chicken, choosing another poultry source like duck may cause a cross reaction. 

Common novel proteins to consider include venison, rabbit, pork, kangaroo or fish. Recommended carbohydrate sources include sweet potato, white potato and green pea. 

Dogcathomeprepareddiet.com is an online resource written by Donald Strombeck, DVM Phd and contains recipes for many home-prepared veterinary diets to meet certain medical needs including skin disease. 

Another site: balanceit.com  can help provide the right supplement mix to home prepared veterinary formulation diet. 

The most ideal way to prepare a home cooked diet of any kind for long-term use is to consult a veterinary nutrition service.  Veterinary schools often have nutrition phone consultations services available.  

It is worth discussing that the FDA has found an association between increased risk of dilated cardiomyopathy (heart muscle disease that can lead to heart failure) and grain – free and boutique diets in dogs.  Grain free diets typically substitute legumes (lentils, peas) or potatoes in place of grains like wheat and corn.  Boutique diets are smaller companies that produce specialty dog foods.  Dogs that benefit from being on a grain- free diet may want to have routine taurine screening or supplementation and careful monitoring for any heart disease symptoms (heart murmur, coughing, exercise intolerance, arrhythmias or fainting).  

Treats and medications for dogs with food allergy

All treats, chews, flavored medications should be discontinued or substituted during the diet trial. For example, no bones, pig ears, rawhide chews biscuits, or table scraps. You can use the new diet as treats(for example the kibble in the dry formulation or by making meatballs of the canned diet, or by baking sliced canned food into cookies.  Other acceptable treats are dried sweet potato treats, carrots, broccoli and apples. 

If you must have a treat option, you can purchase prescription hypoallergenic treats like Hills Hypo Treats or Purina’s Gentle Snackers.

Hills prescription hypo treats

Purina Gentle Snackers hydrolyzed treats

Homemade vegetable treats like dehydrated sweet potato can also be used. 

Flavored oral  heartworm tablets should be switched to top spot applications like Advantage Multi.

After the 8 to 10 week elimination diet trial, your veterinarian may  have you re-incorporate certain foods or simply challenge your dog with their old diet again to determine if the signs recur.

Diagnosis of seasonal allergies (Canine atopic dermatitis)

Seasonal allergy initially presents as a warm weather/seasonal problem in 50 to 75% of cases but can progress to a non-seasonal problem in up to 80% of cases. 

Breeds predisposed to seasonal /environmental allergies:

• West Highland white terrier
• Golden or Labrador retriever
• German shepherd
• Boxer
• French bulldog
• Bull terrier
• Shar pei

Favrot’s Criteria is the  method used by clinicians to help diagnose seasonal allergies in your dog: 

Meeting 5 of 8 criteria gives you an 80% chance of diagnosing environmental allergies in your dog: 

• Onset of signs under 3 years of age
• Dog living mostly indoors
• steroid-responsive itch
• Seasonal itch
• Affected front feet
• Affected ear flaps
• unaffected ear flap margins
• unaffected lower back area

Environmental allergies (seasonal) or food allergies in dogs predominantly cause itchy skin and redness in dogs around their muzzle and eyes, armpits, groin, inside ear flaps and feet.

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When dogs have allergies their skin will become inflamed and itchy. The skin has its own immune function and barriers to infection.  But, as the skin becomes inflamed these natural barriers break down.  This can cause changes in skin and coat quality (dry coats and red, scaly skin) predispose allergic dogs to skin infections. 

Dogs with skin allergies develop: itchy skin with redness, rashes, regions of hair loss, small raised bumps, scabs and flakes. Skin that is itchy and inflamed for long periods of time may become thickened and elephant-like (lichenification) with increased pigmentation.

Have you ever been kept up at night by annoying slurping sounds of your dog working on his toes?  This is one of the more common symptoms of allergies in dogs.  Over time, you may notice your dog’s feet start to bronze from the saliva staining their fur. If it progresses, your dog can develop an infection between their toes. Front feet are more commonly affected than the back feet with seasonal allergies. 

Unlike people, your dog’s skin is uniquely predisposed to developing bacterial skin infections.  Because of the dog’s skin structure and pH, when their skin becomes inflamed from allergies, a bacterial skin infection can develop. This looks like pustules, red patches, and flaky round lesions called collarettes. 

Some dogs will develop ear infections secondary to allergies. Read here to learn about swollen ear flaps as a complication of allergy-induced ear infections.

Treatment for bacterial skin infections in dogs

The most common bacteria that causes skin infections in dogs is called staphylococcus pseudintermedius. First tier antibiotic choices for bacterial skin infections include: clindamycin, amoxicillin-clavulanate and cephalexin used twice daily. If your dog’s skin fails to improve within 7 to 10 days of starting an antibiotic, your veterinarian will likely change the antibiotic class within the first tier choices.  

If the skin infection persists, a skin culture may be performed to screen for a methicillin resistant bacterial infection.  Although resistant skin infections are on the rise in our pets, the good news is that the type of resistant skin bacteria that colonize dog skin:  {methicillin resistant staphylococcus pseudintermedius :MRSP} is unlikely to cause infection in people.  If your dog’s skin culture is positive for methicillin resistant staphylococcus aureus (MRSA: the kind of resistant skin infections seen in people), that skin infection most likely came from you or another person living in your home!

At home therapy options for skin infections in your dog

Topical therapy is recommended for all dogs with bacterial skin infections.  Bathing with a medicated shampoo helps to reduce scales, crusts and grease and also is an antiseptic for the skin. Some of the most effective medicated shampoos use 2-4% chlorhexidine such as Douxo Chlorhexidine PS shampoo.

 If you are trying to use topical therapy alone to treat a skin infection, this is best achieved by bathing your dog daily (a tall order for many owners!). If you cannot bathe your dog daily, then there are chlorhexidine mousses or sprays available.  For example, Duoxo Chlorhexidine mousse and Douxo chlorhexidine spray can be used with the shampo.  Duoxo recommends specific protocols that pair the use of Douxo shampoo with either the mousse or spray. 

DOUXO^® MICROEMULSION SPRAY PROTOCOL (WITH SHAMPOO)

Sample schedule for Douxo shampoo and micro-emulsion spray: 

• Week 1: Shampoo day 1 and spray on days 4 and 7. 
• Week 2:  Shampoo on day 10, spray on days 13 and 16
• Week 3: Shampoo on day 19, spray on days 22 and 25

Sample schedule for Douxo shampoo and mousse: 

• Week 1 : Shampoo on day 1, mousse on days 4 and 7
• Weeks 2 and 3: Mousse on days 10, 13, 16, 19, 22 and 25. 

A home prepared solution that is good for resistant bacterial skin infections in dogs can be made from dilute bleach. This is a very effective topical therapy for resistant bacterial infections : ¼ cup of regular bleach  (5.25% sodium hypochlorite) per half bath (20 gallons).  Soak for 10 minutes and then rinse off.  Be sure to avoid contact with the eyes. 

Causes of recurrent skin infections in your dog

Does your dog have recurrent skin infections? Your veterinarian will need to look for the underlying trigger.   The most common cause for bacterial skin infections is allergy, followed by hypothyroidism and cushing’s disease in dogs. 

The most common causes for recurrent skin infections in dogs are listed below:

• Allergic skin disease (seasonal allergy, food allergy, flea allergy)
  
• Mites (demodex or scabies).   Demodex is far more commonly seen than scabies but is most often seen in dogs under age 1 and in only a few locations. 
  
• Endocrine disorders (for example Cushing’s (hyperadrenocorticism), hypothyroidism or diabetes mellitus). These disorders occur mostly in middle aged to older dogs. 
  
• Keratinization disorders (ichthyosis, sebaceous adenitis, zinc responsive dermatosis, etc.) These disorders are more rare and generally lead to more severe skin signs.

Treatment of environmental (seasonal) allergies: 

Anti itch treatment:

Steroids: steroids have been a mainstay of treatment for allergic pets for years. However, they can have both short and long term side effects.  Short term side effects include increased thirst and urination, panting and hunger.  Long term side effects can be thinning skin, pot bellied appearance, and sometimes skin lesions that cause calcium deposits in the skin. 

Apoquel: specifically inhibits janus kinase 1 in the itch signaling pathway.  It is administered to dogs at 0.4mg-0.6mgkg twice daily for 2 weeks and then once daily  and is reported to be as effective as steroids. 

Side effects: mild increase in diarrhea, vomiting, lethargy or decreased appetite was observed in the apoquel treated study group, but these signs were reported to spontaneously resolve with continued dosing. Long term use warrants regular lab work monitoring to screen liver enzymes as those have also been reported to rise in some dogs treated with apoquel.  There may also be an increased incidence of benign skin bumps called histiocytomas and papillomas. 

Cytopoint: a mono-clonal antibody injection treatment that neutralizes IL-31 which is a potent signaling molecule in the itch cycle.  It can start working within 1 day and can last a month.  It can be re-dosed as needed every 4-8 weeks. 

Side effects: In a field study of 245 patients, adverse reactions happened with the same frequency as those dogs given a placebo injection. 

Allergen specific immunotherapy – desensitization to confirmed environmental pollens, weeds, molds, grasses etc. using injections or sublingual drops tailored to the dog.  This requires a battery of skin testing with a panel of local pollens, weeds, grasses, molds etc. If your dog’s skin develops a raised wheal then this is a positive allergy response to the injected allergen. 

Hyposensitization injections or sublingual drops are 70% effective in 6-12 months. 

Antihistamines for dogs with skin allergies: individual responses to different antihistamines-  trialing different antihistamines over 7 to 15 days is recommended.

• Benadryl 2.2mg/kg twice daily
• Hydroxyzine 2.2 mg/kg twice daily
• Chlorpheniramine 0.5mg/kg twice daily
• Zyrtec : 1mg/kg once daily

Fish oil supplements for dogs with skin allergies:

Fish oils supplements have synergistic effect with antihistamines. Dosing is based on omega 3’s EPA and DHA: Recommended dose is 125mg/kg of EPA/DHA combined. Nordic Naturals is a reputable source of marine fish oil. This article in Today’s Veterinary Practice reviews therapeutic fish oil dosing in our pets.

There are also essential fatty acid top spot pipettes that can be applied topically to improve the skin barrier against infections

Topical shampoo/conditioners active ingredients for skin soothing: 

Topical shampoos or conditioners for dogs may contain some of the following ingredients to help soothe the skin: 

• Benadryl (diphenhydramine): Diphenhydramine reduces histamine release which causes redness and swelling 
• Oatmeal: Colloidal oatmeal binds skin to provide a protective barrier
• Hydrocortisone: Hydrocortisone is a steroid that helps to reduce itch and inflammation
• Pramoxine: Pramoxine is a topical anesthetic that helps to reduce itching
• Ceramides: Ceramides help to lock in moisture by helping to create a skin barrier
• Chlorhexidine: Chlorhexidine is an antiseptic with antibacterial activity
• Chloroxylenol: Chloroxylenol is an antiseptic with antibacterial activity
• Miconazole: Miconazole has antifungal activity
• Ketoconazole: Ketoconazole has antifungal activity
• Phytosphingosine: Phytosphingosine encourages skin repair, has anti-inflammatory and antimicrobial activity 

Topical therapy with weekly shampoos and wiping down your dog’s feet, belly, ears and perineal area when they come in from the outdoors can help reduce absorption of pollens through the skin.  Absorption of allergens across the skin in dogs is a primary mode of starting the allergic response.  A damp cloth or pet antibacterial wipes. Clothing such as cotton t-shirts can also act as a barrier. 

If your dog suffers from bouts of itchy skin, hair loss and skin infections, chances are it was triggered by allergies.  Determining the cause of the allergy is crucial to understanding how best to make your dog most comfortable and reduce recurrence.