Which statement about disinfectants is true?

• A. Disinfectants are more environmentally friendly than detergents.
• B. Disinfectants have a kill time of one minute.
• C. Blood and protein inactivate many disinfectants.
• D. Low- and intermediate‐level disinfectants must be registered with government agencies.

Answer: (C)

Disinfectant effectiveness is strongly influenced by cleaning the surface first, because organic soil like blood and proteins can neutralize or consume the disinfectant and shield microbes. When blood or protein is present, the active ingredients react with these substances, reducing the concentration available to kill organisms and often preventing the disinfectant from reaching all microbes. Cleaning away that soil before disinfection allows the disinfectant to contact microbes more reliably and for the required contact time to be effective. That’s why the statement about blood and protein inactivating many disinfectants is true: removing organic matter improves disinfection performance.

The other points don’t hold as universally. Disinfectants aren’t inherently more environmentally friendly than detergents—many have environmental or health considerations that require careful use and disposal. Kill times vary widely by product, organism, and soil load, so a fixed one-minute kill time isn’t accurate for all situations. While regulatory oversight exists for many disinfectants, the specifics of registration depend on the jurisdiction and product type, so phrasing it as a universal requirement isn’t reliably true.