Final answer:
Allergies are immune reactions that can occur in response to harmless substances. They involve increased numbers of eosinophils, which are immune cells that play a role in allergic reactions and defense against parasitic infections.
Step-by-step explanation:
Allergies are immune reactions that occur when the body's immune system overreacts to harmless substances, such as pollen or food proteins. In these reactions, the immune system produces increased numbers of specific cells, called eosinophils, which are involved in both allergic reactions and the defense against parasitic infections.