Help me understand: 2 severe allergic reactions in 3 years with unknown causes!

Hi! I have a 10-year-old Jack Russell Terrier, and for about three years now, she has been experiencing allergic reactions of an unknown cause. I’m posting here in the hope that someone might be able to offer advice or a different perspective. In 2024 (late April), she had a severe allergic reaction: her muzzle, paw pads, and vulva became swollen, and she developed hives all over her body. She was licking and scratching herself. The reaction started around noon and worsened throughout the afternoon. We eventually gave her cortisone because the swelling and hives were not going away on their own, and by the evening, she was back to normal. At the time, we thought it might have been her kibble, so we switched it. The new kibble contains none of the ingredients from the previous one, but this year, around the same time (late April 2026), she had another allergic reaction—similar to the first one but milder. Her muzzle, three legs, and vulva swelled slightly. She also had raised bumps under the skin, but only on her hind legs, and she wasn’t scratching or licking them. Cortisone was not necessary. The fact that her kibble was completely different from what she had been eating during the first reaction made us think it probably wasn’t food-related. But now we have no idea what could have caused it, and we’re worried it might happen again. I think she may be prone to allergies. She always scratches a little, but it gets much worse in spring and summer. Back in 2019 (five years before the first severe reaction involving swelling, etc.), she had severe dermatitis with scabs and bleeding. At the time, we thought she might be allergic to flea bites because we found a few fleas on her, but we’re not certain. After her most recent allergic reaction involving swelling (April 2026), we had blood allergy testing done. The results showed a “questionable” reaction to grass pollen, while all other environmental allergens tested negative. In short, we don’t know what to do or what might be causing these severe reactions, so we also don’t know how to prevent them. We live in the countryside and try to make sure she avoids tall grass. We also keep her indoors when the grass has just been mowed, but apparently, that still wasn’t enough to prevent this new allergic reaction at the end of April 2026. In both cases, we were not close to her when the reaction started. During the first episode (April 2024), we were away from home and noticed something was wrong about half an hour after it had started. By then, she was already somewhat swollen and had hives under the skin. During the second episode (April 2026), she simply got up from her bed in the morning, walked to the front door, and shortly afterwards came back to my bed. She took two deep breaths and made a retching motion, and after a while, she started swelling up. I was in bed and didn’t see what happened while she was near the door. Now we’re constantly on edge and don’t know whether we can leave her alone, because we have no idea what might be triggering these reactions—other than simple dermatitis. What do you think? What could be triggering reactions like this? I also read online about something called an allergy threshold or tolerance threshold. As I understand it, a dog can “accumulate” exposure to allergens without showing major symptoms until it reaches a critical threshold and suddenly has a stronger reaction—but is that actually true? And after a reaction like this, does the threshold reset? I haven’t been able to find much information about it, and my vet hasn’t been able to give me an answer either. He keeps blaming the food, but during her first severe allergic reaction, she was eating kibble containing chicken, pork, wheat, and corn. Now she eats grain-free lamb kibble (Acana Grass-Fed Lamb), so how could it still be the food? We don’t give her anything else besides kibble and, occasionally, carrots or apples.   Anyway, I apologise for writing so much—and maybe not very clearly—but we don’t know who else to turn to. Even our dog is living with anxiety and stress now because we’re afraid to let her do anything or even allow her to live normally anymore.

Hello and thankyou for this interesting case.  What's striking to me is that although your dog was on different diets when these swellings occured and presumably had eaten the diets at different times of year without issue, she still experienced the signs at the same of year - perhaps this makes a single dietary cause less likely and those causes relating to things that change around April - pollens, perhaps, or insect exposure (including fleas) more likely.  However, it's worth pointing out that allergy is an overreaction of the immune system and can, over the years, generalise to be triggered by more and more things.  Have you ruled out lamb? - dogs can still be allergic to lamb proteins, whatever the sheep were fed on.  However, food allergy is thought to be relatively rare. And sometimes, it is not one trigger but a multitude occuring spontaneously . Sometimes finding an allergen can therefore be very difficult and frequently vets find it more helpful and cost effective to try to control the signs with drugs.  However  If pollen is suspected, rinsing down of paws and the fur after walks has been shown to be helpful; it is handy if a dog will swim in the sea before they return to the house, but this isn't always available! And  plenty of people rinse with buckets.   Keeping the fur short can help to avoid overheating (and thus exacerbating the urge to scratch).  Again, whatever the allergy fleas will always exacerbate the itchiness - and flea allergy itself is definitely a 'thing' - so flea control, both on the patient and in the house - can be extremely important. If you search for 'allergy' within our blog, you might also find some interesting articles about this scratchy subject. I hope that something here is useful.

At the same time of year - correction.  Sorry.

Thank you so much for your reply! So, what would you recommend I do at this point? Should I change her kibble again?   I would also like to add that I checked through my previous kibble orders, and she has actually been eating the Acana food since January 2025 (although last year we did not have any allergic episodes).   In my previous message, I did not mention that among the allergy test results, she came back as strongly allergic to beetroot, carrot, potatoes, and yeast, while grains were marked as “uncertain.” I did not mention this earlier because I know food allergy tests are not always considered reliable, but I wanted to add this information to give a more complete picture. I should also add that she absolutely loves carrots, and we used to give them to her every day as a snack. I know it is impossible to say for certain, but do you think this could have played a role in the allergic reaction she had in April 2026?   At the moment, we are rinsing/washing her every time after walks, and we are also giving her omega-3 and Ribes nigrum (blackcurrant) drops. Do you think these supplements could help increase her reactivity threshold? (I am not sure if that is the correct term.)   One last thing... My biggest fear is that, since we have not fully understood what is causing this angioedema-like reaction, it could eventually happen again in a much, much more severe way. Do you think this is a real possibility? (Even though this year’s reaction was milder than the first one in 2024.)   I have honestly become almost paranoid about it... I know this is not good for my dog, but these severe and unpredictable reactions really scare me, to the point that I am even afraid to leave her home alone for too long because I cannot monitor her. Thank you so much again for your time and advice — I really appreciate it.