Fleas do not wait for summer. Eggs hatch once the ground holds 10 to 13°C for a few days, so a warm March week starts the cycle while the cat is still indoors. Begin prevention 4 weeks before your area's average low passes 10°C, and keep it going 12 months a year if this house has had fleas within the last 2 years.
The lifecycle that explains every failure
An adult female lays 20 to 50 eggs a day, and the eggs fall off wherever the cat sleeps. They hatch in 2 to 5 days into larvae, which burrow into carpet fibre and feed on flea dirt for 5 to 11 days before spinning a cocoon. The pupa is the problem: it can stay dormant for up to 6 months, surviving vacuuming, cold and most sprays, and it hatches when it senses warmth, vibration and carbon dioxide.
Only about 5 percent of an infestation is on the cat. Roughly half is eggs, about a third larvae, and a tenth pupae, all in the environment. Treating the cat alone removes that 5 percent and guarantees a second wave 2 to 3 weeks later, which people read as "the product stopped working".
Year-round versus March to October
Seasonal treatment works only if you start early and stop late. The classic failure is stopping in November: pupae from autumn overwinter indoors, and the first warm days hatch a cohort onto an unprotected cat. A heated house never gets cold enough to break the cycle, which is why indoor-only cats get fleas too — the fleas arrive on your shoes, on a visiting dog, or through a shared hallway.
Year-round prevention costs $144 to $300 a year for one cat. A household infestation costs $200 to $600 in products plus 6 to 8 weeks of daily vacuuming, and often a $150 vet visit for the dermatitis it triggers. The arithmetic favours year-round in any home with carpet or a dog.
Treat the environment, not just the cat
- Vacuum daily for 14 days, under furniture and along skirting boards; warmth and vibration wake dormant pupae.
- Seal the bag or empty the canister into an outdoor bin after every session.
- Wash all bedding at 60°C for at least 10 minutes, including your own duvet.
- Use a product containing an insect growth regulator (IGR) such as methoprene or pyriproxyfen; an adulticide alone leaves the pupae.
- Treat the gaps between floorboards, the car the cat travelled in, and any fabric cat bed.
- Repeat environmental treatment at day 14 and again at day 28.
Foggers are poor value: they do not reach under furniture or into the base of carpets, and they drive the cat out of the room you need to treat. Mechanical removal plus an IGR does more.
Pollen season does not look like sneezing
Cat pollen allergy shows as itching, not respiratory signs. Watch for chin and muzzle rubbing, scabby ear pinnae, licking between the toes until the fur thins, and symmetrical hair loss along the flanks. It starts in the same weeks each year and eases indoors with windows shut and a HEPA filter running. Wiping the coat with a damp cloth after outdoor access removes a large share of the pollen load before the cat grooms it off.
Flea allergy dermatitis looks different again: crusts and hair loss at the tail base, the back of the thighs and the belly, plus miliary dermatitis — small crusts like millet seeds across the spine. A single bite sets it off in a sensitised cat, so seeing no fleas does not rule it out.
Food allergy is year-round
If the itching never stops, suspect food. Food allergy in cats usually targets the head and neck, often comes with vomiting or soft stool, and does not follow the calendar. Chicken, fish and beef are the common triggers in commercial diets; an 8-week elimination trial on a novel protein or hydrolysed diet is the only way to know, and treats must be included. A cat that itches only from April to September has an environmental problem.
Permethrin kills cats
Never apply a dog flea product to a cat. Permethrin at the concentrations in dog spot-ons — often 45 to 65 percent — causes tremors, hypersalivation, twitching, hyperthermia and seizures in cats, sometimes within 1 to 2 hours of contact. Cats lack the liver enzymes to clear it, and the dose in a single large-dog tube is many times a lethal exposure for a 4 kg cat. This includes "natural" dog sprays and dog shampoos.
If it happens, wash the cat with lukewarm water and mild dish soap immediately, without scrubbing the skin raw, and phone the vet or a poison line the same hour. Do not wait for symptoms, because by the time tremors start the drug is already distributed. Other household toxins are covered in poisoning first aid. Cat-safe actives include fipronil, selamectin, imidacloprid and indoxacarb, dosed by weight.
Choosing a product by weight, not by guess
| Product | Safe for cats | Notes |
|---|---|---|
| Fipronil spot-on | Yes | Monthly; separate tubes for under 4.5 kg and over |
| Selamectin spot-on | Yes | Monthly; also roundworm and ear mite |
| Imidacloprid | Yes | Adult fleas only, no egg control |
| Permethrin dog spot-on | No — toxic | Never, not even a partial tube |
| Ordinary flea collar | Weak | Patchy coverage, neck area only |
| Flea shampoo | Short-lived | No residual; useful only as a bath before an IGR |
| Oral flea product | Vet decision | Check the label for cat approval and weight band |
Dose by measured weight, not by eye. A 4.4 kg cat and a 6 kg cat need different tubes, and splitting a large-dog pipette is not a substitute for a cat product. Full parasite timing sits in fleas and worms.
Five steps for the first warm week
- Weigh the cat and buy the correct weight band of a cat-only product.
- Set a monthly reminder on the same date, and record the date applied.
- Vacuum daily for 14 days and wash every cat bed at 60°C.
- Book a vet visit if the itching is on the face, ears or between the toes, and photograph it weekly.
- Check every dog product in the house and move it out of reach of the cat cupboard.
Frequently asked
My cat never goes outside. Can it still get fleas?
Yes, and indoor-only cats are common cases. Eggs and pupae survive in the hallway, on shoes, on a visiting dog and in second-hand soft furnishings, and a heated flat never gets cold enough to break the cycle. If a neighbour's dog or a shared stairwell has fleas, your indoor cat can be the first in the building to show dermatitis.
Do I need to treat the house if I only see one flea?
Yes. One adult on the cat implies roughly 20 times that number in the environment, in the egg, larval or pupal stage. Vacuum daily for 14 days, wash bedding at 60°C, and use a product with an insect growth regulator. Skipping the environment is the main reason people report that flea treatment stopped working.
How can I tell pollen allergy from a food allergy?
Timing and location. Pollen allergy follows the season, year after year, and usually shows on the face, ears, paws and flanks. Food allergy runs all year, often affects the head and neck, and is frequently accompanied by vomiting or soft stool. An 8-week elimination diet is the only reliable test, and it has to include every treat.