Why Does My Cat Still Have Fleas After I Used Frontline?

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According to Frontline's website, Frontline does not repel fleas, so they are still attracted to cats that have been treated. New fleas are killed when they come into contact with the pet's coat, but it can take up to 24 hours for the new fleas to die. However, if the Frontline applied was expired, it may not work at all; in this case, the pet owner must wait 30 days to apply it again.