As we have said, the presence of a few adult fleas does not mean your topical flea product is not working. You should be concerned your flea product is not working if you find large numbers of fleas, flea dirt and flea eggs on your pet’s coat. We have another blog about how to look for evidence of fleas here. Often it can take time to treat your pet’s environment to eradicate evidence of fleas.
Cats can be better at removing the evidence of fleas, but look for signs of overgrooming, such as stubbly hairs at the tail base. Look for evidence of flea dirt in areas your cat cannot reach, such as the back of their neck, or around their ears.