A small study looked at how to identify food allergies in dogs with atopic dermatitis, a common itchy skin condition. Researchers tested 12 dogs by adding small amounts of eight common food items, like beef and chicken, to their special diet for one week each. They also gave the dogs a placebo, which was just their regular diet mixed with water, to see if reactions were real.
They found that most dogs (11 out of 12) reacted to between one and six of the food items. However, half of the dogs that reacted to real foods also reacted to the placebo. This means some of the 'allergic reactions' might have been due to the placebo effect, where a dog or its owner expects a reaction and sees one, rather than a true food allergy.
The study was very small and did not report specific numbers for how strong the reactions were. The main reason to be careful is that this placebo effect creates doubt about how accurate food allergy tests are, both in this study and in previous ones that didn't use a placebo. Readers should understand that identifying food allergies in pets can be tricky, and this research highlights why controlled testing is important, even though more work is needed.