Why Did The Topical For Fleas On My Cats Didn't Last All Month?

Why Did The Topical For Fleas On My Cats Didn't Last All Month?
Can fleas become resistant to treatment?
Can I put flea medicine on my cat more than once a month?
Why is flea treatment not working on my cat?
Is there a long lasting flea treatment for cats?
How do you get rid of fleas that won't go away?
Do fleas get worse after treatment?