If you inhaled some pollen and started sneezing, you would know that it was an allergic reaction. You would also know that this seasonal allergy feels different to a food allergy. Your dog can tell the difference too, but your dog is obviously unable to tell you the suspected cause of their allergy. Since seasonal allergies and food allergies present many similar symptoms, it's up to you to tell the difference, like you're playing a strange game of charades with your dog.
The Immune System
Just like humans, dogs can experience both seasonal allergies and food allergies. When their body is exposed to an allergen, their immune system responds, and this response is the allergic reaction. A food allergy is similar, although it occurs when your dog's immune system misidentifies a protein in their diet as an allergen and reacts accordingly. What are some of the signs of these respective allergic reactions, and what action do you need to take?
Itchiness and general discomfort are key signs of both a seasonal and a food allergy. Your dog may appear uncomfortable and will repeatedly (and vigorously) scratch and lick themselves. You're really looking for secondary symptoms, and this is where the difference becomes more clear. Some form of respiratory distress is common with a seasonal allergy, but not with a food allergy. But since the food allergy is a response to something that has been consumed, your dog may become nauseous and will often have diarrhoea.
See Your Vet
Whether the allergy is seasonal or food-based, your dog might require medical attention, depending on the severity of their symptoms. While a vet can often distinguish a seasonal allergy from a food allergy, they may wish to confirm this with a test. In most cases, a radioallergosorbent (RAST) test will be sufficient, and this requires a blood sample. More detailed testing is also possible, and this is known as an intradermal skin test. This test is only recommended when the allergy is thought to pose a significant health risk, as it's quite an intensive process, and requires your dog to be sedated.
An Elimination Diet
When the allergy is confirmed as seasonal, antihistamines can be prescribed. Just as with humans, canine antihistamines will then be taken as needed. When a food allergy is suspected, your vet will recommend an elimination diet. This is a basic diet combining both a basic protein and carbohydrate, utilising sources that have not been part of your dog's regular diet. This should ideally remove the problematic protein from rotation, eliminating future instances of food allergies.
Your Dog's Ongoing Diet
Moving forward, your vet will make some clear recommendations for pet food for your dog. This can be a commercial brand designed to give your dog all their required nutrients while limiting the ingredients to a basic protein and a carbohydrate source. Your vet will give you a few different available options, and then it's simply a matter of ditching the mass-produced supermarket food for a specialist brand that eliminates the problematic allergen.
So while there are some key differences between a seasonal allergy and a food allergy, your vet may need to confirm the nature of the allergy so its source can be addressed.