Trigemic vapors were gases found on some planets, which caused skin irritation in humanoids. Their effects could be ameliorated by dermal osmotic sealant. Trigemic vapors left a residue of proteins and amino acids.

"Planet Hell" in the Delta Quadrant contained high levels of trigemic vapors in its atmosphere. The vapors were the sole source of nourishment for newly hatched Repto-humanoids. (VOY: "Parturition")