Fleas came back after treatment? Here's why

That returning infestation two weeks after treating your dog is one of the most common flea frustrations — and it almost always comes down to the same thing: the home wasn't treated at the same time. Up to 95% of a flea population lives in carpets, bedding, and soft furnishings, not on the dog itself. So even a perfectly treated dog gets reinfested within days by eggs and larvae already hatched in the house. To point you to the right fix, can you tell me: how old and how heavy is your Irish Setter, how bad are the fleas right now — are you seeing them on the dog, in the house, or both — and have you tried treating your home at all yet?

That explains it exactly — the spot-on did its job on her, but the house is still the source. At 27kg she's a large dog, so dosing isn't the issue here. The reinfestation is coming straight from your soft furnishings. Before I get to the home treatment, is she on any regular flea prevention, and do you know which spot-on you used? Some are stronger than others, and at 8 years old I want to make sure we're not doubling up on anything that could cause a reaction.

Frontline Plus is fine for her — it's a solid choice for a healthy adult dog her size. The honest truth is that treat-when-you-see-them doesn't quite work with fleas, because by the time you spot them the house is already seeded with eggs. But let's fix the immediate problem first, then we can talk about keeping on top of it going forward. For the home, the product I'd point you to is Indorex Defence Household Flea Spray. It contains permethrin to kill adult fleas on contact, plus an insect growth regulator — pyriproxyfen — that stops eggs and larvae from developing for up to 12 months. One 500ml can treats up to 130 square metres, which covers most houses. You spray carpets, skirting boards, under furniture, and any soft furnishings your Setter uses. Vacuum thoroughly first to stimulate any dormant pupae, then spray and leave it to dry. The pupae stage is flea-proof to sprays, so you may still see a few adults hatch over the next week or two — that's normal, and they'll die quickly once they contact the treated surfaces.

Keep her out of the treated rooms until everything is fully dry — usually around an hour in a well-ventilated space. Open windows while you spray and let it air out properly. Once dry, it's safe for her to be back in normally. Just wash her bedding on a hot wash the same day you spray, and if she has a fabric collar or soft harness, wash those too. Don't spray it directly on her — it's a home treatment only. After that, I'd genuinely suggest moving her onto a monthly flea preventative rather than waiting to see fleas again. Frontline Plus monthly is fine, or if you want something stronger for a dog her age who's clearly being exposed, a vet-prescribed product like Bravecto or NexGard would give you longer-lasting cover. But the Indorex is the urgent step right now.

One application of Indorex is usually enough — the growth regulator keeps working for 12 months so you don't need to retreat unless you have a very heavy infestation and keep seeing live adults after two to three weeks. If fleas are still very active after three weeks, a second spray is reasonable. The main thing is keeping her on monthly spot-on treatment consistently from here, because that breaks the cycle from the other end. Sort the house today, keep her treated monthly, and this should be the last time you're in this situation.