Insecticial soap is defined as any of the potassium fatty acid soaps used to control many plant pests. Insecticidal soap is typically sprayed on plants in the same manner as other insecticides. Insecticidal soap works only on direct contact with the pests. The fatty acids disrupt the structure and permeability of the insect cell membranes. The cell contents are able to leak from the damaged cells, and the insect quickly dies.