The fatty acids (propionic, caprylic, and undecylenic) and their salts have been available and widely used for the past 15 years in the form of proprietaries for the treatment of superficial fungous infections. Also, undecylenic acid was at one time administered by mouth in huge doses and for long periods as a hopeful, but vain, treatment for psoriasis.
To date we know of no published reports of proven sensitization to any of these agents. (In conversations with colleagues we were told of instances in which they thought they had encountered sensitization effects from commercial preparations of the anti fungal fatty acids and their salts, but they had never taken the trouble to prove or disprove the possibility of sensitization to the agents or to the vehicles that carry them.) Following is a report of a case of allergic eczematous contact dermatitis caused by sensitization to undecylenic acid and its zinc
MELVIN GELFARB, MORRIS LEIDER. Allergic Eczematous Contact DermatitisReport of a Case Caused by Sensitization to Undecylenic Acid and Its Zinc Salt. Arch Dermatol. 1960;82(4):642–643. doi:10.1001/archderm.1960.01580040160033