My cat, Atticus, took a “vacation”. He got out Thanksgiving night and returned three weeks later. Luckily, he did not have fleas, but he had ticks. I bought Hartz Ultra and applied it. He started to lick it immediately, but I thought it was because it was on his fur. Two days later, he licked himself bald. I Googled and came across this site. Im devastated and feel awful for this guy. I rescued him a year ago, he is FIV positive and 11 years old. He has enough to deal with. Im calling the vet tomorrow. I applied diluted lavender oil to ease the irritation. I hope it helps.