Which of the following is true about disinfectant effectiveness?

The correct answer focuses on the fact that disinfectants become inactive when contaminated with hair, dirt, or debris. This is crucial because the presence of organic material can shield microbes from the disinfectant's active ingredients, reducing its ability to effectively destroy pathogens. For disinfectants to be effective, surfaces must be clean and free from any organic material. This emphasizes the importance of proper cleaning procedures prior to disinfection to ensure the highest level of microbial control.

Other answers highlight points about disinfectants but do not capture the critical condition for their effectiveness as well. For instance, while frequently used disinfectants can maintain their efficacy depending on their formulation and concentration, proper cleaning is essential to achieve disinfection. Similarly, the effectiveness may diminish when products are expired, but this highlights the importance of shelf life rather than the immediate application condition. Finally, while some disinfectants may be effective when diluted, this does not represent a universal truth; many disinfectants are specifically formulated to be used at a concentrated level to ensure full efficacy against pathogens.