What is the most common protein dogs are allergic to?

The most common proteins to cause a reaction in dogs are chicken and beef. It’s important to keep in mind that this doesn’t mean they’re what your individual dog is intolerant to. There is nothing in either chicken or beef that makes them inherently more likely to cause an allergy or intolerance - rather it is because they are most commonly used across all types of dog food so, statistically, more dogs are exposed to them. For dogs fed on processed food, such as kibble, chicken or beef may be the only protein they’re fed, making a food intolerance more likely to develop.