Caterpillar dermatitis and fiber glass (Fiberglas) dermatitis can be diagnosed with certainty when caterpillar hair or fiber glass filaments are demonstrated in skin scrapings. The latter are treated with 20% KOH or NaOH and examined microscopically.
Fisher BK. Diagnosis of Uncommon DermatosesAdditional Uses of a Simple Office Procedure. Arch Dermatol. 1969;99(2):152-153. doi:10.1001/archderm.1969.01610200024004