Allergens are

Options

A. Certain microbes which are pathogenic
B. Weak antibodies produced by certain substances in the body
C. Weak antigens which produce sensitive reactions in the body
D. None of these

Answer

**Step-by-Step Solution:**

1. **Definition of Allergens**: Allergens are specific substances that can trigger an allergic reaction in sensitive individuals. They are typically harmless to most people but can provoke an immune response in those who are allergic.

2. **Nature of Allergens**: Allergens can be various types of substances, including pollen, pet dander, certain foods, dust mites, and even some medications. They are not limited to microbes; they can be any substance that elicits an allergy.

3. **Mechanism of Allergic Reaction**: When a person who is sensitive to a particular allergen comes into contact with it, their immune system mistakenly identifies it as a threat. This leads to the production of antibodies, specifically Immunoglobulin E (IgE), which triggers the release of chemicals like histamine, resulting in allergic symptoms.

4. **Symptoms of Allergic Reactions**: The symptoms can range from mild (sneezing, itching, rashes) to severe (anaphylaxis). The severity depends on the individual and the amount of allergen exposure.

5. **Clarification of Misconceptions**: Allergens are not pathogens (disease-causing microbes) nor are they weak antibodies. They are considered weak antigens because they provoke an immune response without being harmful in most cases.

6. **Conclusion**: Therefore, allergens can be defined as weak antigens that produce sensitive reactions in the body, leading to allergic responses in susceptible individuals.

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