After repeated exposure, which group of substances will cause an allergic reaction?

• A. Carcinogens
• B. Sensitizers/Allergens
• C. Irritants
• D. Convulsants

Answer: (B)

Repeated exposure can train the immune system to treat a substance as a threat, so the body mounts an allergic reaction upon later contact. Substances that are sensitizers or allergens do just that: after initial exposure, the immune system becomes primed, and subsequent exposures trigger immune-mediated symptoms such as dermatitis, rhinitis, or asthma.

Carcinogens are linked to cancer risk rather than allergy. Irritants can cause irritation, and sometimes reactions occur without prior sensitization, meaning they don’t rely on the immune system recognizing a specific substance. Convulsants affect the nervous system and do not cause an allergic immune response.

So, substances that are sensitizers or allergens best fit the idea of triggering an allergic reaction after repeated exposure.