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LOAEL, or Lowest Observed Adverse Effect Level, is the smallest exposure in a study at which adverse effects are observed. In risk assessment, this point helps establish protective exposure levels by applying uncertainty factors to account for differences between animals and humans and to extrapolate from study conditions to real-world, longer-term exposures. When a NOAEL isn’t available, LOAEL can still be used to derive a reference dose, but with additional safety factors because adverse effects were seen at that level, making the estimate more conservative. This term is distinct from No Observed Adverse Effect Level, and it isn’t simply the lowest contaminant amount in air or a universal “level of allowed risk” for compliance.