Indoor contamination from microorganisms is an important health hazard issue (e.g., respiratory allergy, infections, and food contamination). Particularly, growth of molds and bacteria in damp environmental conditions could be hazardous for the occupants susceptible to microbial allergens. The growing awareness concerning the adverse effects of chlorine bleach and cleaning chemicals calls for field-testing new natural ingredients with functional properties against microorganisms. Essential oils possess a wide spectrum of antimicrobial activity, which may be of great importance for controlling indoor microbial exposure. The objective of this study was to investigate how microbial growth in different surfaces of homes reacted to the application of natural products serving as a health harmless aid to rid the home of microorganisms. The natural products consisted of tea tree oil, natural vinegar, and grapefruit seed extract, which demonstrated antifungal properties in our other studies. To assess microbial load before and after treatment of the natural products, ATP levels were monitored. ATP released from microorganisms produces light in the presence of luminescence enzymes and the intensity of this light can be measured with a luminometer and can be quantified as Relative Light Units (RLUs). Each natural product was used in between pre-treatment and post-treatment swabbing of the suspected damp surfaces (toilets and windows) in home environments following a standard CDC protocol and levels of ATP in swab extracts were measured by a luminometer. Results showed a consistent 10-times decrease in the ATP analysis of the toilet after using all three natural products, although pre-treatment recordings took place above the threshold. The window had sort of an opposite effect due to an increase being noted in the ATP analysis containing the natural products tea tree oil and vinegar. However, a 56% decrease was noted in the ATP analysis of the window after use of the grapefruit seed extract.