i know some chemical pesticide that once treated lice on humans was banned in the 70's... the web says pesticides can cause al sorts of problems: cancer seizures, vomiting, spinal problems, painful skin leisions, neurological issues, behavioral changes...
Nonetheless, ticks and or fleas can carry harmful and deadly diseases such as lyme disease to name one.
I just applied Advantage to my sisters yorkie who I am babysitting..and she started pacing around the apartment and walking in circles looking nervous and upset..so i read the label on the box and learned there was a pesticide as the active ingredient. After a little internet research realized other dogs do the same thing when their owners put advantage on them and that some dogs have died from it! so I wiped it off of her with soaked paper towel. She stopped pacing but now she is laying down in the other room gloomily and disgruntled. Poor thing. I hate seeing her suffer and am paranoid now because she has soooo many problems that could be linked to the advantage. she has had a major behavior change over the years, she has skin lesions, liver problems, has a crooked back when she goes to the bathroom and sometimes when she lays down, she has had a seizure, and she vomits sometimes... Now I am going to have to explain to my sister that she should find another method of prevention...even though she has spent thousands of $$ on her already...ahh what a headache. I dont want her getting lyme disease either though...
Check this site out for natural remedies:
Natural Flea & Tick Prevention Program | Homeopathic Flea & Tick Remedies For Pets | Organic Flea & Tick Alternative