Specific Target Organ Toxicity

By Tabitha Mishra
Last updated: February 26, 2024

What Does Specific Target Organ Toxicity Mean?

Specific target organ toxicity (STOT) refers to the adverse, non-lethal health effects of a toxic substance that affect an organ and its functions.

Safeopedia Explains Specific Target Organ Toxicity

The Globally Harmonized System of Classification and Labeling of Chemicals (GHS) categorizes the specific target organ toxicity of various substances according to the type of exposure, the target organ, and the severity of the effects.

Since humans cannot be subjected to significant harm in laboratory settings and data on exposure to toxic substances is limited, many of the STOT classifications are based on animal studies.


STOT- single exposure (STOT-SE) refers to the adverse, non-lethal, organ-specific health effects of a toxic substance that manifest following a single exposure.

Toxins with STOT-SE effects include:

  • Neurotoxins that target the central nervous system, such as mercury, acrylamide, and carbon disulfide
  • Respiratory toxicants that target lung tissue, such as asbestos and silica
  • Hepatotoxins that target the liver, such as nitrosamines and carbon tetrachloride
  • Nephrotoxins that target the kidneys, such as certain halogenated hydrocarbons
  • Hematopoietic agents that impede the function of hemoglobin and prevent oxygen from reaching blood tissues, such as carbon monoxide and cyanides

These toxins fall under three hazard categories:

  • STOT-SE 1 (H370, signal word “danger”): known to be toxic to humans from a single exposure
  • STOT-SE 2 (H371, signal word “warning”): presumed to be toxic following single exposure
  • STOT-SE 3 (H335 and H336, signal word “warning”): irritant or narcotic effects


STOT – repeated exposure (STOT-RE) refers to the adverse, non-lethal, organ-specific health effects of a toxic substance that only manifest after multiple exposures.

The GHS divides STOT-RE into two categories:

  • Category 1: Substances that produce significant toxicity in humans after repeated exposure
  • Category 2: Substances that are presumed to be harmful to humans after repeated exposure, based on findings from animal studies

There are two hazard categories in this classification:

  • STOT-RE 1 (H372, signal word “danger”): known to be toxic to humans after repeated exposure
  • STOT-RE 2 (H373, signal word “warning”): presumed to be toxic after repeated exposure

GHS STOT Pictograms

In order to quickly convey the level of risk associated with substances with STOT effects, the GHS uses pictograms to indicate the hazard category.

For the more hazardous STOT Category 1 and Category 2, the pictogram for health hazards is used:

GHS health hazard symbol

For the more benign STOT Category 3, the exclamation mark pictogram is used:

GHS exclamation mark symbol

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