Though the most common issue associated with fleas is increased itching and scratching in your pet (and sometimes family members, too!), unfortunately, more serious problems can occur from a flea infestation.
Not only can fleas make your pet uncomfortable, but some pets can also have a serious allergy to flea bites. This condition, called flea allergy dermatitis, can lead to lingering issues, even long after the fleas have been killed. The pet may experience “hot spots” triggered by secondary infections. Allergies to fleas can also trigger other secondary conditions, including ear inflammation of the middle ear or mild forms of gastrointestinal distress.
Additionally, fleas can carry and transmit tapeworms to both humans and pets. Fleas have also been shown to be able to spread certain bacterial diseases, most famously the bubonic plague.
Though serious complications are rare, it is much easier to prevent these issues from happening than it is to try to treat them after they’ve occurred.