Which of the following can cause Eosinophilia?

Eosinophilia, which is an increase in eosinophils in the bloodstream, can be caused by several factors, and one of the primary triggers is type I hypersensitivity reactions. These reactions are characterized by an allergy or anaphylaxis situation where the body encounters an allergen, leading to the activation of mast cells and the subsequent release of various inflammatory mediators. Eosinophils are part of the body's immune system response, particularly in reactions involving parasites and allergic conditions such as asthma, hay fever, or anaphylaxis. Their elevation in such scenarios is a direct consequence of the allergic cascade triggered by immunoglobulin E (IgE), which leads to the recruitment and activation of eosinophils to the site of inflammation.

While other conditions can also contribute to eosinophilia, such as certain infections or neoplasms, type I hypersensitivity specifically describes a clear and direct mechanism by which eosinophil levels rise in response to allergens. The other options, such as chronic kidney disease or hyperthyroidism, may have more complex pathways for inflammation or immune response which do not directly correlate with the isolated increase of eosinophils typically seen in allergy-related conditions. Iron deficiency is generally associated with microcytic anemia and