Indoor cats get fleas mainly because fleas are very good at entering homes and finding hosts, even when the cats do not go outside. Fleas can jump indoors through open doors and windows, even passing through insect screens. They locate hosts by sensing body heat, vibration, and breathing, then jump onto the cat to feed on its blood. Other common ways fleas reach indoor cats include:

• Other pets in the house that go outside and then bring fleas inside.
• Visits to places like a vet, groomer, boarding facilities, or shelters where fleas might be present.
• Contact with local wildlife or rodents around the home.
• Flea eggs and larvae already present in carpets, furnishings, and the indoor environment, where flea life stages can live dormant and hatch later.

Fleas are tiny, can jump far, and hide well under the cat’s fur, so even indoor cats can quickly become infested if preventative measures are not taken year-round.