Mike,
There are some reports of sensitivity to certain topicals but the real toxicity comes with tick dips and tick collars. I think the probability of your dog contracting Lymes, or E. Canis is much higher than having any issues with a topical (Frontline or Advantix). If you use Hartz or lesser products the chances of reactions are higher.
I don't think there is any long term study...but if your dog tolerates the application process and has no signs of sensitivity...it is well worth it because of the tick borne diseases.
Dr.V
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Dr. D.A. Vamvakias
Veterinarian
