When do fleas die after being treated with drops on the neck? - briefly
Fleas usually die within 30 minutes to a few hours after a neck‑drop medication is applied, depending on the active ingredient and dosage. Complete removal from the host typically occurs by the end of the first day.
When do fleas die after being treated with drops on the neck? - in detail
Fleas exposed to a spot‑on treatment applied to the cervical region begin to lose motor function within minutes. The insecticide spreads through the skin’s lipid layer, reaching the hemolymph and disrupting neural transmission. Most adult fleas are immobilised and die within 4 – 6 hours. Residual activity continues to affect newly emerging fleas for up to 30 days, depending on the formulation.
Key factors influencing the mortality timeline:
- Active ingredient – fipronil, imidacloprid, selamectin and nitenpyram act at different speeds; nitenpyram produces the fastest knock‑down (15–30 minutes), while fipronil and imidacloprid require several hours for full effect.
- Flea life stage – adult fleas are killed rapidly; eggs and pupae are insulated from direct contact and may persist until they hatch, after which they are exposed to the residual drug.
- Hair length and skin condition – dense or oily coats can slow diffusion, slightly extending the time to death.
- Environmental temperature – higher ambient temperatures accelerate metabolic rates, shortening the lethal interval.
Typical mortality schedule for a standard fipronil‑based product:
- 0–30 minutes – initial paralysis in a minority of fleas.
- 30 minutes–2 hours – progressive loss of mobility; most begin to fall off the host.
- 2–6 hours – majority are dead; dead fleas may be found on bedding or floor.
- 6–24 hours – remaining survivors eliminated; environmental re‑infestation prevented by residual activity.
«The systemic spread of the compound ensures that any flea feeding within the treatment window receives a lethal dose». Proper application – a single dose at the base of the skull, avoiding contact with eyes or mouth – maximises absorption and ensures the described timeline. Continuous monitoring of the pet’s environment, combined with regular cleaning, supports the pharmacological action and reduces the risk of reinfestation.