During the twentieth century, many new human-made materials have been developed, often leading to only subsequent understanding of the damaging effects these have on human and environmental health. This chapter traces the key patterns in historical and recent recognitions of harmfulness of human-made substances used in building materials. It uses the history of the past recognition to propose a need for insisting on an improvement in the way human and environmental health are considered when developing new materials including ecomaterials. By systematically reviewing past and current examples, it is possible to demonstrate that the existing processes do little to prevent the introduction of harmful substances into manufacture. Consequently, any development of new materials should actively include consideration of the impacts of human and environmental health in early stages of the design of materials. To illustrate this, the chapter uses a range of examples from well-recognized problems with lead and asbestos to currently poorly recognized risks of nanotechnology, biopolymers, and ongoing use of substances with mild but suspected adverse health impacts. The overall conclusion is that so far, human society has been slow to recognize the health risks, and even when these were reasonably known, the new chemicals entered prolific productions without adequate effort to consider or eliminate such risks. The existing patterns of slow recognition of health risks should be broken by calling for earlier and more comprehensive investigations of totality of likely impacts new materials present for the human environment and health.