[citation needed] Insecticidal soap's active ingredient is most often a potassium salt of fatty acids.
Certain types of household soaps (not synthetic detergents,[6] ) are also suitable, but it may be difficult to tell the composition and water content from the label.
According to one study[14] a single soap application killed about 15% of lacewing and lady-beetle larvae, and about 65% of predatory mites (Amblyseius andersoni).
Among green peach aphids that are in contact with a 2% soap solution, around 95% of the adults and 98% of nymphs die within 48 hours.
[4][5] In the European pesticide registration, its use as an insecticide is listed for aphids, white fly, and spider mites.
[12] Insecticidal soap solution will only kill pests on contact; it has no residual action against aphids that arrive after it has dried.
Highly sensitive plants include:[4] horse chestnut, Japanese maple (Acer), Sorbus aucuparia (mountain ash), cherimoya fruit, Lamprocapnos (bleeding heart), and sweet pea.
Other sensitive plants include:[9][4] Portulaca, some tomato varieties, Crataegus (hawthorn), cherries, plum, Adiantum (maidenhair fern), Euphorbia milii (crown of thorns), Lantana camara, Tropaeolum (nasturtium), Gardenia jasminoides, Lilium longiflorum (Easter lily).
[citation needed] Thanks to its low mammalian toxicity, application of insecticidal soap is typically allowed up to the day of harvest.