I had a similar problem with Frontline Plus but with the dogs loosing hair in patches and we checked the diet, blood tests, skin scrapping etc., with no conclusion so I decided to take my dogs off Frontline because I could not think it could be anything else. I use Advocate made by Bayer here it costs double what Frontline costs but it control fleas, heart worm, intestinal worms, demodectic mange, sarroptic mange, ear mites and lice. And weighing up the cost of taking the dog to the vet with skin problems caused by Frontline I thought Advocate the better option. They have been using it for 18 months (older dogs) with no problems. Vets tend to promote products and sometimes without checking whether they are good or not. I also think it depends on the breed we used Frontline on our smaller dogs and never had any side effects. Maybe they have changed the ingredients? Who knows.