Most cats and dogs can support a few fleas without trouble. But if your pet comes inside carrying a new batch of fleas several times in a row, you have a serious flea problem in the yard, or at least in the area frequented by your pet.
In humans, flea bites vary in effect from short-lived itching welts to an overall rash to symptoms which may last over a year, depending on the sensitivity of the victim. Young children are more sensitive than older persons. A small red spot usually appears where the skin has been pierced. The wound does not swell very much, but a red halo of irritated skin surrounds the spot and usually lasts for several hours to a day. In pets, fleas can cause constant scratching, and without treatment this can lead to skin infections, hair loss, and other problems. Pet owners who routinely comb their pet with a fine flea comb from time to time are in the best position to know when a flea problem may be developing outside in the yard.
White sock trick: If you suspect there may be some flea areas in your yard, put on a pair of knee-high white athletic cotton socks to go with your sneakers. Walk around slowly in the suspected areas and if adult fleas are present some will jump up on the socks where they are easily spotted. Alternatively, wrap fly paper (sticky side out) around your lower legs and count fleas adhering to it after a predetermined time interval