Answer:
MCUs are a type of polyurethane that is used to coat wood floors in homes. They make a very durable and scratch resistant finish and are often used on gymnasium and bowling alley floors.
Exposure to MCU chemicals can lead to health effects depending on the level and duration of exposure. Brief exposures to elevated levels can result in headaches, respiratory irritation, and exacerbation of asthma; while very high and/or long-term (e.g. lifetime) exposures can lead to more serious health effects.