This may not be a question that you have asked yourself before, but it is definitely a good one that warrants looking at more often. This is because you have to understand your enemy in order to beat it, and fleas are an enemy that is hard to get rid of at the best times. All the research will tell you that of course, so let’s take a look at understanding just how fleas go from dogs to people and cause no end of trouble along the way.
Fleas come from outside
Fleas get into your home by hitching a ride on your dog. Fleas are very common in the tall grasses and other areas that most gardens or parks have. Your pet will love exploring these areas, so it is easy enough for fleas to find a way into your home. They can also grab hold of your shoelaces or the hems of your trousers and come in that way, too.
Dogs and cats are easy carriers
This is true.  Fleas can hide easily in the fur of your pets, so remember this and make sure you treat your pet regularly to make sure that s/he is pest free. This includes grooming and washing, when possible.
Fleas make a home inside
From your pet, fleas will find a place to live in your house and start an infestation that can rage on for a while and you won’t even know that it’s happening. Fleas are tiny and hard to detect, not to mention that a flea can lay up to 800 eggs in her lifetime. They’re hard to stop once they start.
They carry pests of their own
Including tapeworms, fleas can have all sorts of nasties on board, plus bacteria, that can be transferred from them to their host. And don’t fool yourself, fleas can use humans as hosts too. We just don’t always notice them, or we think we’ve been bitten by other insects. 
Allergic reactions
It is possible to have a severe allergy to the saliva of fleas, which is life threatening in many cases. While this is in regards to humans, cats and dogs can also die from fleas if the infestation is strong enough. Fleas cause a lot more than just itchiness, and it quickly becomes a human problem.