Animals also have allergies just like human beings. Animals react to physical agents like humidity, cold, drafts, air, heat and dampness and that's why some time they have loss of appetite. It is however very difficult to identify allergies in animals if you are not used to them.
Yes, lots of animals are allergic to everyday items. They can be allergic to plants, foods and even other animals. You can go to the vets and get your animal tested to see if or what they are allergic to. Hope this helped ;)