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A sensitizer is defined by OSHA as "a chemical that causes a substantial proportion of exposed people or animals to develop an allergic reaction in normal tissue after repeated exposure to the chemical."

The condition of being sensitized to a chemical is called chemical hypersensitivity.

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Certain chemicals have no immediate health effects. But if you are exposed to them several times, they can make you allergic or sensitive to other chemicals, often quite suddenly. A classic example is formaldehyde (CH2O). Typical reactions to sensitizers can include skin disorders such as eczema and respiratory disorders such as asthma.

Sensitization is an immune response. Therefore, some people may be easily sensitized while others may never be affected. Like any allergic response, a reaction to a sensitizer can be fatal in rare circumstances. You can not predict your reaction to sensitizing chemicals, so treat all sensitizers with great respect and follow proper chemical safety and hygiene procedures.

Once you are sensitized to a particular chemical, even minute amounts will cause symptoms. Sensitization is usually a life-long effect, so avoid working with such substances even if you have suffered no ill effects in the past.

Traditionally, sensitization has been determined using animal testing. On April 10, 2018, the US EPA released a draft Science Policy to reduce the use of animals in testing chemicals to evaluate whether they cause an allergic reaction, inflammation or sensitization of the skin. The draft policy is open for public comment until June 9, 2018. The document is titled Draft Interim Science Policy: Use of Alternative Approaches for Skin Sensitization as a Replacement for Laboratory Animal Testing and describes the science behind the non-animal alternatives that can now be used (in vitro, in silico, in chemico) to identify skin sensitization. The US EPA currently requires these data to support pesticide registrations. Public comments on docket # EPA-HQ-OPP-2016-0093 can be submitted via during the comment period.

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SDS Relevance

The hazard classification process required under Appendix A of the OSHA Hazard Communication Standard covers respiratory and skin sensitization at Paragraph A.4. Substances with high frequency of occurence of human sensitization are classified as sub-category 1A, and those with low to moderate frequency are classified as sub-category 1B. When data are not sufficient for these determinations, the substance is classified as Category 1.

The pictogram used for Category 1 skin sensitizers is an exclamation mark and for respiratory sensitizers is the health hazard symbol, both of which are shown below and are available from our retail partner, Safety Emporium.

However, if the health hazard pictogram is included for respiratory sensitization, then the exclamation point pictogram will not appear on the label where it is normally used for skin sensitization or skin or eye irritation. This hierarchy is designed to keep labels uncluttered, so be sure to remind yourself that if it's bad to inhale a substance, it is probably bad to get on your skin!

Avoid working with sensitizers whenever possible. If you have no viable substitute and you must work with a sensitizer, use a fume hood or other type of engineering control if available. The SDS should list appropriate personal protective equipment such as gloves or even a respirator, so be sure to use the recommended type of each!

Further Reading

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See also: asthma, irritant, urticaria

Additional definitions from Google and OneLook.

Entry last updated: Wednesday, April 11, 2018. This page is copyright 2000-2019 by ILPI. Unauthorized duplication or posting on other web sites is expressly prohibited. Send suggestions, comments, and new entry desires (include the URL if applicable) to us by email.

Disclaimer: The information contained herein is believed to be true and accurate, however ILPI makes no guarantees concerning the veracity of any statement. Use of any information on this page is at the reader's own risk. ILPI strongly encourages the reader to consult the appropriate local, state and federal agencies concerning the matters discussed herein.