What might cause a homeowner to notice unusual smells after cleaning?

Residual cleaning products or trapped contaminants being disturbed is a common reason homeowners notice unusual smells after cleaning. When cleaning, particularly deep cleaning, many products are used that can leave behind residues. These residues can emit odors as they dry or when disturbed. Additionally, if there are contaminants like dust, mold, or other particulates trapped in air ducts or surfaces, cleaning can agitate these substances, releasing trapped odors into the air. As the system moves air, these smells can become noticeable throughout the home.

The other options, while they may contribute to odors in other contexts, do not directly relate to the immediate aftermath of cleaning. For instance, fresh air entering the home typically leads to improved air quality rather than unusual smells. Pest infestations might lead to smells but are less likely to correlate directly with a cleaning session unless specific pest control products are used. Improper ventilation could cause issues over time, but it does not explain the immediate odors following a cleaning effort.