A non-infectious unnatural and unusual reaction of a person to any substance or condition for which he is hypersensitive is termed as

Options

A. Immunity
B. Allergy
C. Infection
D. Toxin

Answer

To answer the question, we need to analyze the terms provided and identify which one fits the description of a non-infectious, unnatural, and unusual reaction of a person to any substance or condition for which they are hypersensitive.

### Step-by-Step Solution:

1. **Understanding the Question**:
- The question describes a reaction that is non-infectious, unnatural, and unusual, indicating that it is not caused by pathogens like bacteria or viruses.

2. **Identifying Key Terms**:
- The terms "non-infectious" and "hypersensitive" are crucial. They suggest that the reaction is related to the immune system's response to typically harmless substances.

3. **Evaluating the Options**:
- **Immunity**: This refers to the body’s ability to resist infections and diseases. It does not fit the description since it is a protective response rather than a reaction.
- **Allergy**: This is a hypersensitive reaction of the immune system to a substance that is usually harmless, such as pollen or certain foods. This matches the description perfectly.
- **Infection**: This is caused by pathogens and is infectious, which contradicts the non-infectious aspect of the question.
- **Toxin**: This refers to poisonous substances that can cause harm, but it does not relate to the hypersensitivity aspect described.

4. **Conclusion**:
- Based on the evaluation, the correct answer is **allergy**. An allergy is indeed a non-infectious, unnatural, and unusual reaction of a person to substances to which they are hypersensitive.

### Final Answer:
A non-infectious unnatural and unusual reaction of a person to any substance or condition for which he is hypersensitive is termed as **allergy**.