Permethrin is a synthetic chemical widely used as an insecticide. It belongs to the pyrethroid family, mimicking natural insecticidal extracts from chrysanthemum flowers. Permethrin is incorporated into numerous products for pest control, from agriculture to household use and treated clothing.
Permethrin’s Biological Action
Permethrin primarily acts on the nervous system of insects. When an insect comes into contact with or ingests permethrin, the chemical interferes with its nerve cells. It targets voltage-gated sodium channels, causing them to remain open and leading to a continuous influx of sodium ions.
This disrupts normal nerve impulse transmission, resulting in muscle spasms, incoordination, and paralysis. Insects are more susceptible than mammals because their sodium channels are more sensitive and they metabolize the chemical less efficiently.
Onset of Effects
Permethrin acts rapidly on insects, often showing effects immediately upon contact. This quick action, known as “knockdown,” incapacitates insects soon after exposure. For instance, ticks on permethrin-treated clothing are affected immediately, often flipping backward and rolling off.
Nymph deer ticks have been observed to die within a minute of contact. The visible signs vary from immediate paralysis to death, depending on the insect species, size, and permethrin concentration.
Rapid incapacitation prevents insects from biting or causing further harm. This makes permethrin effective for preventing bites from pests like mosquitoes, ticks, and lice. For head lice, permethrin lotion is typically left on the hair and scalp for about 10 minutes to destroy lice and eggs.
Lasting Effectiveness
Permethrin exhibits residual activity, remaining effective on surfaces after application. The duration varies significantly by application method and environmental conditions.
On plants, permethrin may remain active for 1 to 3 weeks. Indoors, it can persist on surfaces for over 20 days, with some studies reporting detection in house dust for years.
On treated clothing, permethrin binds to fabric fibers, offering prolonged protection. Factory-treated clothing can maintain effectiveness through up to 70 washes. Exposure to sunlight and washing gradually reduce permethrin concentration over time.
Factors Affecting Performance
Several factors influence permethrin’s performance, affecting both action speed and duration. Higher concentrations generally lead to more rapid effects. The specific formulation (spray, dust, treated clothing) also impacts interaction with insects and the environment.
Environmental conditions like temperature and humidity influence stability and activity. The type and life stage of the target pest matter, as different insects have varying sensitivities. Material type for treated items also affects how well permethrin binds and persists.
Application and Safety Guidelines
When using permethrin products, follow all label instructions. Wear appropriate personal protective equipment, such as gloves, and ensure adequate ventilation in enclosed spaces.
Permethrin is poorly absorbed through human skin and is generally considered safe when used as directed. Avoid direct contact with eyes or accidental ingestion.
Permethrin is highly toxic to cats and aquatic life, including fish and bees. Prevent exposure to these non-target organisms by keeping cats away from wet applications and avoiding water source contamination. Common applications include treating clothing for mosquito and tick protection, perimeter sprays, and topical treatments for human parasitic infestations under medical guidance.