Production and use of chlorophenols (CPs) are being phased out around the globe, but with considerable lag in some highly populated countries. The process could be incentivized by leading countries sharing their experiences on problems that occurred, including the built environment. We previously reported that Swedish industry and authorities promoted CPs, including pentachlorophenol (PCP), as wood preservatives in buildings for decades. Yet, Swedish indoor research did not recognize exposure to the hazardous CPs and their odor potent derivatives, the chloroanisoles (CAs), which smell like mold and still evolve from legacy preservatives in damp building structures. We hypothesized that the toxic CPs and odorous CAs could be key players for health and odor problems not only in Sweden but also in the neighboring Nordic countries. We found no reports in scientific medical literature of CPs being used in buildings in these countries. However, grey literature shows that CPs were indeed used, even during building booms, in house exteriors, constructions, and interiors, from the 1950s up to the late 1970s (Denmark) and even the 1990s (Finland and Norway). One application of CPs was in houses erected on dampness-prone house foundations, conditions ideal for formation of odorous CAs through microbial methylation. Furthermore, our searches suggest that these problematic chemicals played hitherto unrecognized key roles when indoor air research evolved. Thus, odor became an important aspect of the “sick building syndrome” in Denmark and an early warning sign of health risks in Finland, as asthma and allergy were attributed to “dampness and mold.” None of the countries addressed the possible links between odor and health effects and exposure to CAs and CPs. In conclusion, our results suggest that unrecognized indoor exposure to toxic CPs and odorous CAs has mislead Nordic indoor air research for decades.