Pictogram 7: Health Hazard - Respiratory Sensitizer

Pictogram 7, the Health Hazard pictogram, includes respiratory sensitizers.

As you have already learned, the HCS defines "sensitizer" as a chemical causing "a substantial proportion of exposed people or animals to develop an allergic reaction in normal tissue after repeated exposure to the chemical."

The Society for Chemical Hazard Communication (SCHC) defines a respiratory sensitizer as "a chemical that will lead to hypersensitivity of the airways following inhalation of the chemical" and notes that "in contrast to respiratory irritation, respiratory sensitization is an immunological response to previous exposure to a chemical. Hypersensitivity is normally seen as asthma, but other hypersensitivity reactions involving the nose (rhinitis), eyes (conjunctivitis), or lungs (alveolitis) are also considered."

The SCHC notes that previous exposure to a substance is necessary for respiratory sensitization to occur. The sensitization occurs in the following two phases:

1. Induction (or sensitization): The development of specialized memory cells in the immune system of an individual occurs after the initial exposure to a respiratory sensitizer.
2. Elicitation: An allergic respiratory reaction occurs after exposure to a respiratory sensitizer. The specialized memory cells (produced in the individual's immune system following the initial exposure) respond to the subsequent exposure; for example, an allergic reaction takes place.

A chemical is classified as a respiratory sensitizer if there is proof that the substance can lead to specific respiratory hypersensitivity in humans (and, optionally, if there are positive results from an appropriate animal test).

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