Extended habitation of space may include the cultivation of plants for atmospheric regeneration, water purification and food production. Plants produce bioactive compounds that may be released into the atmosphere as volatile organic compounds (VOCs). VOCs are produced through a variety of plant processes and vary greatly in chemistry and quantity though a plants life cycle. These compounds include numerous biogenic species including alcohols, isoprene, monoterpines, acids, carbonyls, alkanes and alkenes. In a closed environment, VOCs may create a toxic environment for either humans or other plants. Human responses to biogenic compounds may include acute toxicity, chronic toxic toxicity, and allergenic effects. Chronic exposure to low concentrations of biogenic compounds, as might be common during extended space habitation missions, is largely unstudied and of particular interest. The objectives of this paper are to provide an overview of the salient issues regarding potential production of biogenic VOC's, to identify potential responses of humans to these compounds and to assess the overall risk of exposure using epidemiological methodologies. A series of monographs were developed for the most common biogenic VOC's produced for Advanced Life Support (ALS) candidate crops. The monographs describe the compounds, reported sources, SMAC or TLV exposure limit (if established), and reported human responses and toxicity levels. In addition, biogenic responses on plant production systems are reported, if known. Finally, an assessment of potential risk on long duration habitation missions is provided.