The truth of the matter is that if you have cats that live outdoors and indoors, you are likely to find fleas around the home or on the cat at some point in their lives. People who are new to cat owning may wonder whether they can be dangerous to humans or not. Fleas are parasites, and they will feed on the blood of any warm-blooded animal that they happen to land on. There are a lot of bacteria that fleas can transfer, such as tapeworm and murine typhus, through rats. However, they are rare for humans to get from fleas.
Fleas will bite humans, and they can get inflamed and itchy. When fleas bite cats and dogs, their saliva can cause dermatitis, and their waste has had similar effects on humans. So, while they are not exactly dangerous, they are often very annoying.