What is a characteristic behavior of sensitizers?

Sensitizers are substances that can lead to an allergic reaction upon repeated exposure. The key characteristic of sensitizers is that the initial exposure may not induce any symptoms; however, subsequent exposures can trigger an immune response due to the body's sensitization to the substance.

This process typically occurs because the immune system develops a memory of the sensitizing agent, which allows for a stronger and often exaggerated response during future encounters. This is particularly relevant in various industries where certain chemicals are used frequently, highlighting the importance of recognizing and managing exposure levels to prevent allergic reactions.

The other choices do not accurately describe the behavior of sensitizers. While some sensitizers might be harmless in low doses or after limited exposure, they can become harmful with repeated contact. Additionally, not all sensitizers are used in medical treatments, as many are chemicals in industrial settings. Lastly, sensitizers fundamentally rely on repeated exposure to elicit an allergic response, contrasting with the notion of requiring only a single exposure to cause reactions. Thus, the defining characteristic of sensitizers is indeed their ability to cause allergic reactions after repeated exposure.