Believe it or not, some people have asked whether or not fleas have the ability to live inside humans similar to tapeworms. Tapeworms are parasitic infections of the digestive tract. Fleas do not feed off anything in our intestinal tract nor do they find the interior of the human body to be all that hospitable.
However, dogs and cats can often get tapeworms by ingesting fleas containing tapeworm larvae. As their body consumes the flea and digests it, the flea then releases the tapeworm and infects the animal.
Fleas on humans? Yes.
Fleas in humans? Absolutely not.
Fleas are an external nuisance and not an internal contaminant, virus or illness. Fleas can burrow themselves underneath the skin and cause infections and other assorted maladies, but they do not live inside the body in a literal sense. See the picture below: