Feline Atopic Skin Sensitivity (FASS)
A Step-by-Step Guide to Diagnosing and Managing Your Cat’s Allergies
Is your cat constantly itching, over-grooming, or developing mysterious scabs? These could be signs of Feline Atopic Skin Sensitivity (FASS)—a frustrating allergic condition that requires patience and a strategic approach. In this guide, we’ll walk through the step-by-step process veterinarians use to diagnose and manage FASS, so you can help your feline friend find relief.
Topics Covered
What is Feline Atopic Skin Sensitivity (FASS)
Step 1: Ruling Out Other Causes of Skin Issues
Step 2: Exploring Food Allergies
Step 3: FASS (Feline Atopic Skin Syndrome) Management:
What is Feline Atopic Skin Sensitivity (FASS)
Itching, hair loss, over-grooming, or sores and scabs are some of the common symptoms your cat might show if they’re struggling with allergies. This condition, known as Feline Atopic Skin Sensitivity (FASS), is essentially your cat’s immune system overreacting to everyday substances in their environment – things like pollen, dust mites, or mold. Just like humans with hay fever, except instead of sneezing, cats tend to take it out on their skin.
FASS can be frustrating for everyone involved – your uncomfortable cat, your worried family, and your veterinarian who wants to provide relief. What makes it particularly challenging is that there’s no quick fix; management requires long-term therapy and a true team effort between you and your veterinary team. The good news? With a systematic approach, most cats with FASS can achieve significant relief. Let’s walk through how we approach a suspected skin allergy case in our feline friends!
Step 1: Ruling Out Other Causes of Skin Issues
Before we can blame allergies, we need to play detective! Many conditions—from pesky fleas to stubborn fungal infections—can mimic FASS symptoms. Think of this step as ‘eliminating the usual suspects’ so we don’t miss something simpler (and often treatable!). Here’s what we check first:
1. Rule out Dermatophytosis (Ringworm or Other Fungal Infections)
Fungal infections (in particular Ringworm) can cause similar skin issues to FASS but the treatment is different so confirming it or ruling it out is important. A fungal culture or PCR test involves taking some samples from your cat’s skin and hair to check for this infection.
2. Ectoparasite Trial
Some external parasites like fleas, mites (e.g., Demodex), or ticks can cause intense itching and skin damage. Even if no obvious parasites are observed during an exam, treatment is recommended because some parasites aren’t easy to spot, especially mites, and cats are great groomers that can groom fleas and flea debris away. A good parasite control product, like Revolution Plus, is essential.
3. Treat Secondary Skin Infections
If your cat’s skin has developed sores or scabs, there could be secondary bacterial and yeast infections making things worse. Skin cytology is an easy in-clinic test to check for infections which may require antibiotics and antifungal treatments. This is important because infections can make your cat’s allergic symptoms harder to manage.
Step 2: Exploring Food Allergies
If your cat’s itching continues after ruling out infections and parasites, and especially if your cat’s symptoms are year-round, food allergies may be to blame. Like humans, cats can suddenly react to ingredients they’ve eaten for years—even common proteins like chicken or beef. Pinpointing the problem requires patience and a strict elimination diet trial, but the payoff is worth it: many cats find lasting relief once we identify the trigger.
How Elimination Diets Work:
An elimination diet helps ‘reset’ the clock by feeding your cat a special diet that only includes ingredients they haven’t had before, to see if the itching improves after a few weeks.
This special hypoallergenic diet contains either:
🔹 Novel proteins (like rabbit or duck) your cat has never eaten before, or
🔹 Hydrolyzed proteins (broken down so small the immune system doesn’t recognize them as allergens).
This strict diet trial lasts at least 8–12 weeks to see if symptoms improve. Even tiny bites of their old food (or treats!) can skew results, so consistency is key!
Our Recommended Hypoallergenic Diets for Trials:
🔹 Royal Canin HP Hydrolyzed Protein
🔹 Royal Canin Anallergenic
🔹 Hill’s z/d Skin/Food Sensitivities
Want to dive deeper into food allergy testing for your cat?
The Canadian Academy of Veterinary Dermatology (CAVD) offers excellent visual guides on elimination diet trials—including how to strictly manage your cat’s food, avoid cross-contamination, and interpret results. These resources complement our in-clinic guidance: 1. Detailed Diet Trial Guide for Cats (In-depth FAQs and troubleshooting) 2. Illustrated Diet Trial Handout for Cats (Simple step-by-step with visuals)
Step 3: FASS (Feline Atopic Skin Syndrome) Management
When all other causes are ruled out, we’ve arrived at FASS—a chronic but manageable condition. While there is no “cure,” most cats achieve excellent comfort with proper management. Success depends on collaboration: we will provide medical expertise, while your observations at home help us fine-tune treatment for your cat’s unique needs.
1. Short-Term Management
To help relieve your cat’s discomfort while other tests and treatments are ongoing, we might suggest medications to reduce itching.
🔹 Corticosteroids (like prednisolone) are often used as a first-line treatment to quickly relieve itching and inflammation. They help give your cat some immediate relief while figuring out the root cause of the allergies.
2. Long-Term Management
FASS is a chronic condition that requires ongoing care. Your vet will help create a treatment plan tailored to your cat’s needs. This will likely include:
🔹 Antipruritic Medications: These medications will help keep the itching under control in the long run. Your vet might suggest alternative medications that work differently than steroids, such as Cyclosporine or Oclacitinib, which can reduce the need for corticosteroids.
🔹 Environmental Allergy Testing: FASS is often triggered by environmental allergens like pollen, mold, or dust mites. Your vet might recommend allergy testing to identify what’s triggering your cat’s symptoms so that specific treatment can be designed. This could lead to immunotherapy (allergy shots or oral drops) to help your cat’s immune system adjust to these allergens over time.
3. Ongoing Steps
The process of managing FASS often requires revisiting the previous steps. If you notice your cat’s symptoms worsening or new symptoms appearing, your vet may need to go back to Step 1 and rule out other causes again. It may take some time to get the right balance of treatments that work for your cat.
Even after your cat’s condition is under control, regular monitoring is essential. Cats with FASS may have flare-ups, especially if they’re exposed to new allergens or if secondary infections occur (often from scratching open their skin, creating a gateway for bacteria or yeast).
Keeping your cat on a regular parasite prevention schedule, like using Revolution Plus, will help reduce the chances of parasites making the symptoms worse. Working closely with your vet and following the treatment plan will give your cat the best chance for a comfortable life despite their allergies.
While FASS requires ongoing attention, many cats live happily and comfortably with the right care plan. If you notice changes in your cat’s symptoms or have questions about their treatment, don’t hesitate to reach out to our team. Together, we can keep your feline friend feeling their best—itch-free and full of purrs
– The Yonge Sheppard Animal Hospital Team ʕ •ᴥ•ʔ