O-Phthalaldehyde (OPA) is a chemical reagent that forms fluorescent conjugation products with primary amines. It is used for the detection of many biogenic amines, peptides, and proteins in nanogram quantities in body fluids. O-Phthalaldehyde is approved by FDA for use in test systems to detect blood urea nitrogen (BUN) for the diagnosis and treatment of certain renal and metabolic diseases. OPA is also a known desinfectant and has been approved for high-level sterilization of heat-sensitive medical instruments and is increasingly being used as a replacement in the healthcare industry for glutaraldehyde. OPA has also been approved for use as an indoor antimicrobial pesticide; an intermediate for the synthesis of pharmaceuticals, medicines, and other organic compounds.

4-Amino-2-Hydroxytoluene is a substituted aromatic compound used in the formulation of permanent hair dyes, colors and tints. 4-Amino-2-Hydroxytoluene is used as a coupler in cosmetic hair dye formulations. The compound has a low oral toxicity in animals and has no significant mutagenic or teratogenic effects. The compound, at most, is a weak skin and eye irritant and, at most, a weak sensitizer. Carcinogenic skin painting studies of hair dyes containing this compound were negative. A variety of epidemio-logic studies have given no indication of a carcinogenic effect from the use of hair dyes.