Hazard classes such as acute toxins, carcinogens, irritants, mutagens, and reproductive toxins are well known, but don’t overlook the insidious nature of respiratory and skin sensitizers.
A sensitizer is a substance that can lead to an allergic response following contact. When you become sensitized to a substance, your immune system develops a memory to the specific agent. With every subsequent exposure, it takes less of the substance to initiate the allergic reaction and the result may be more severe.
Examples of chemical sensitizers include: allylic and benzylic halides; aromatic amines; diisocyanates; epoxy resin components; formaldehyde; nickel compounds; certain cosmetics, fragrances, and preservatives; and the catechol in poison ivy and poison oak.
In a recent case of life-threatening anaphylaxis induced by amino acid coupling agents, the sensitized researcher can no longer work in a research lab. (McKnelly, K. J.; Sokol, W.; Nowick, J. S. “Anaphylaxis Induced by Peptide Coupling Agents: Lessons Learned from Repeated Exposure to HATU, HBTU, and HCTU” J. Org. Chem. 2020, 85, 1764–1768. https://doi.org/10.1021/acs.joc.9b03280)
Bulk material sensitizers include: flour, latex rubber, metals (nickel in particular), wood dusts, and even certain fabrics.
Enzymes can be sensitizers too! In a recent case, a lipase was found to be a potent respiratory hazard. Handling of the enzyme required specialized facilities to minimize operator exposure during scaleup. (Beauchamp, T. J., et al. Org. Process Res. Dev. 2025, 29, 889. https://doi.org/10.1021/acs.oprd.4c00539)
For a review on enzyme sensitizers, see: Baur, X. “Enzymes as occupational and environmental respiratory sensitisers” Int. Arch. Occup. Environ. Health 2005, 78, 279−286. https://doi.org/10.1007/s00420-004-0590-6
The good news is that you can protect yourself from sensitizers using good lab hygiene practices, including wearing gloves, working in a fume hood, and washing your hands every time you leave the lab.
