Fleas can come from a variety of sources, including other animals, outdoor environments, and even inside your own home. They can easily jump from one host animal to another, which is why pets are often a common source of flea infestations. Outdoor areas such as parks, yards, and wooded areas can also be sources of fleas, as they can attach to clothing, shoes, and pet fur. Additionally, fleas can also be brought into the home on infested items such as rugs, furniture, and bedding. In some cases, even a single flea can lead to an infestation if it is able to lay eggs and reproduce. It's important to take preventative measures such as regularly treating your pets with flea preventatives, vacuuming frequently, and washing bedding and other items regularly to reduce the risk of flea infestations in your home.