cat flea treatment

Question
Dr, I realize this question isn't specifically a dermatological question, but fleas can be all-encompassing, beginning with the skin and coat. I would appreciate your view on flea control as I have asked:
This is the first time I've used the flea control that you quirt onto the cat's neck and back area.  I have difficulty seeing how such a tiny amount can control pests for a month.  My cat is extra large, too!  Also, can you tell me once I apply it can I allow my cat to wonder around outside?  He loves to go outdoors occasionally, and I feel sorry for him staying inside all the time.  He IS NEUTERED, so that's not a concern.  I just want a safe, happy cat with NO FLEAS this year!!  Thanks!

Answer
Depending on which topical flea treatment you use, they do spread all over the cat's body.  Some act by getting into the fatty tissue just below the skin, some act by crystallizing on the skin and others act by becoming part of the secretions from the skin's oil glands.  The products from a vet are much better than the ones that are over the counter because they last so much longer.

All of these act by causing immediate toxicity to the flea(s) when they jump on the cat.  It can take about 2 hours to cause the flea to stop biting and 24 hours to kill the flea.  Most of the fleas feed for 3 days before laying eggs, so by killing the baby fleas right away before they lay eggs, you are preventing new fleas from hatching out of eggs.