According to the Household Hazardous Waste Project, synthetic air fresheners do not freshen household air at all.  They simply mask one odor for another, while diminishing one’s sense of smell with an onslaught of “other” chemicals. Synthetic fragrances are not regulated because their formulations are considered ‘trade secrets.’ Many synthetic fragrances are petrochemical derivatives laced with endocrine disrupting compounds, such as phthalates, added to make the synthetic odor linger once emitted into the air.