## **Core Concept**
A nasal smear is a diagnostic tool used to examine the nasal mucosa for various conditions, including allergic reactions and infections. The presence of eosinophils in the nasal smear is indicative of an allergic response. Eosinophils are a type of white blood cell that plays a crucial role in fighting parasites and in allergic reactions.

## **Why the Correct Answer is Right**
The correct answer, **C. Allergic Rhinitis**, is right because allergic rhinitis is characterized by an allergic inflammation of the nasal passages. This condition is often associated with an increased number of eosinophils in the nasal smear. Eosinophils are attracted to the site of allergic inflammation by chemokines and contribute to the symptoms of allergic rhinitis, such as nasal congestion, sneezing, and rhinorrhea.

## **Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the condition described is not specified, making it impossible to assess its relevance to eosinophilia in a nasal smear.
* **Option B:** This option is incorrect because, although infections can cause inflammation, the specific association with increased eosinophils in a nasal smear is more characteristic of allergic reactions than infections.
* **Option D:** This option is incorrect because, while asthma is an allergic condition, the question specifically asks about nasal smears, which are more directly related to conditions affecting the nasal passages, such as allergic rhinitis.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the presence of eosinophils in a nasal smear is a useful diagnostic clue for allergic rhinitis. A nasal smear showing more than 10% eosinophils is often considered positive for allergic rhinitis. This test can help differentiate allergic rhinitis from other causes of nasal symptoms.

## **Correct Answer: C. Allergic Rhinitis**