This article is from the Fleas, Ticks, and Your Pet FAQ, by tittle@zmall.com (Cindy Tittle Moore) with numerous contributions by others.
There are several ways to kill or discourage fleas. Some are synthetic
chemicals, some are considered "natural", and both work with varying
degrees. No one method is 100% effective, and you will almost always
have to combine several approaches to get the results you want. Some
methods are applicable for indoor pets, but useless for indoor/outdoor
pets. You need to choose the set of approaches that best addresses
your situation.
Keep in mind that there are regional differences among fleas: what
works well in one area may not work well in other areas. You should
consult a LOCAL vet, vet tech, or dog groomer to see what is known to
be effective in your area. If you thinkyou're getting biased opinions,
ask several people and see what they concur on. Don't rely on the
products available at your local store; there are too many that are
just distributed nationally.
Finally, you may find that you need to switch your approaches around
from year to year. If you use the same product several years in a row,
you may find the effectiveness lessened. Additionally, some years are
worse than others, depending on the previous winter, and you may need
to strike earlier with stronger methods some years and relax a bit
more with milder methods another year.
 
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