Thursday, May 23, 2024
HomeCatsQ&AWhy Does My Cat Still Have Fleas?

Why Does My Cat Still Have Fleas?

Fleas are a problem in most parts of the world, but especially in warm humid areas, and particularly in high density living. If you’re like most cat owners, you probably think that once your cat is on a good flea control protocol, they should be flea-free. Unfortunately, this isn’t always the case. Here we talk about why that happens and what you can do to give everyone some relief.

If we step back and think about them, fleas are fascinating parasites. They are also very successful at what they do, which of course makes them difficult to control. It would be nice to think we could just put a monthly flea product on our pet then forget about it, but environmental treatment is also important. If you are after a more natural approach we will also give a few recommendations of what will and won’t work for your pet.


Most flea products will kill adult fleas and stop them laying more viable eggs. Only 5% of the flea population actually lives on your pet, so if you are seeing 5 fleas, it means that there is another 95 fleas living in the environment.  You are only seeing the tip of the iceberg. The tiny eggs, larvae or pupae live in the environment, commonly concentrated around resting areas. This means there are usually plenty of new fleas to replace those fleas on your pet that are being killed by your flea product. In addition, many products take hours or days to kill each single flea, so you can still see up to 20 fleas on your pet even though the product is working. Check out this video of the flea life-stages.


After a flea jumps onto your cat, the flea starts feeding on blood and laying eggs. A female flea can lay up to 50 eggs a day, so it is no wonder you can go from one flea to hundreds in a very small space of time, and why being late with flea medications can be a big problem.

The eggs fall off your pet and hatch within 1-10 days (quicker if it is warm and humid). The hatched larvae move somewhere dark (usually downwards into gaps between floorboards, in soil, under mulch, deep in carpet or bedding or under furniture), where they feed on organic material (including flea faeces). After 5-11 days the larvae pupate, forming a sticky cocoon around themselves which protects them and makes them difficult to target with vacuuming or a flea bomb. After 7-10 days the fleas will hatch in response to vibrations, carbon dioxide or heat and go searching for a blood meal. If there is no stimulation to hatch, these fully developed fleas can stay in their cocoons for years. Which is why in some cases you can move into a vacant property and have a big flea emergence all at once.

Under most circumstances, biting people is a last resort for fleas; they would much prefer to live on our pets than bite us. In warm humid conditions the flea cycle is very fast, and the whole thing is completed within 2 weeks. It slows down or stops altogether with dry, cold or very hot weather.


Generally most cats can tolerate low numbers of fleas, so seeing a couple of fleas is not necessarily cause for alarm. If you are using a flea product, most likely those fleas are slowly getting poisoned and are on their way out. It is a different story for those cats that are allergic to flea bites. Flea saliva allergies are very common in cats. These unfortunate pets tend to scratch and chew, particularly around the base of the tail and often develop quite nasty hot spots or skin infections.

In flea allergic pets just one flea bite can keep them itching for 2 weeks. A flea can bite up to 400 times before it is killed, so even just one flea can lead to big discomfort. These cats really need strict flea control, both environmental and frequent topical or oral application. In very small kittens, large numbers of fleas can also lead to anaemia from fleas feeding on their blood. Fleas also spread some blood-borne diseases and tapeworm.


Flea shampoos and powders are very ineffective and a waste of time and money. The effects only last for as long as the substance stays in the coat, so one or a few days is all you get. Unfortunately flea control really is one of those things where you get what you pay for. Some topical or oral flea products can be expensive, but if you use them properly and throughout the year, combined with good environmental control, you will avoid the hassle and expense of employing a professional pest exterminator and costly veterinary bills from skin problems.

As mentioned previously, flea products for the most part don’t work instantly. The only repellent-style products available are Pyrethrim-based such shampoos and these are very toxic to cats. For all other products (Frontline Plus, Advantage, Advocate, Comfortis and Revolution) the fleas must either bite your pet to ingest the toxin or absorb the toxin from contact with your pet’s skin, so you can see how a flea allergic pet will often have a problem if there are large numbers of newly emerged fleas in the environment. For these cats, the aim is to reduce environmental flea numbers AND treat your cat.

Products with Nitenpyram (like Capstar) have a faster speed of kill, than most top-spot products so if you are seeing large numbers of adult fleas on your pet, give them a Capstar tablet. It can be used in conjunction with all other flea products, but the effects only last for 24 hours, so it is impractical to use it as your sole form of flea treatment. The newest flea product out is called Comfortis. This monthly flea tablet starts working within hours, so it is the fastest acting monthly flea treatment currently available.  Ask your vet if you would like to try Comfortis.


Frontline Plus is stored in the sebaceous (oily) glands in the skin, so frequent bathing or swimming (more than weekly) can strip it from the skin and mean it is less effective. It is very important not to apply it just after a bath, and you cannot bathe your cat for 48 hour after using it. Frontline Plus has the advantage that the toxin used is not absorbed significantly by your cat, so if you are reluctant to use toxins in your pet, perhaps Frontline Plus is a good compromise.


There is no actual reported resistance to flea medications according to the manufacturers of these products. There certainly are products that work better in certain situations though. The manufacturers of Frontline in particular have done extensive research into the topic, including getting samples of fleas from all over the US. They have found no resistance problems, but report that most product failure is usually due to improper application or lack of concurrent environmental control.


First look at where your pet spends most of his time. Target this area in particular. Use a flea bomb inside the house to get rid of those eggs and larvae that will hatch and repopulate your pet. You can also get a hand held spray to treat underneath cupboards, couches and beds. A flea bomb will keep working for 9 months.

If you are not keen to flea bomb, consider frequent vacuuming every 3 days. Also vacuum before the flea bomb and remember that those larvae are motile, so you will need to vacuum under furniture. Pay particular attention to pet sleeping areas. You will not necessarily vacuum up the fleas unless you have an industrial strength vacuum, as the flea cocoons are sticky, but vibrations of the vacuum will stimulate the fleas to emerge from their cocoons, and it is these cocoons that protect the pupae. Vacuuming also gets rid of flea faeces and other organic material from the floor that the larvae feed on.

You can also use a powder called Flea Busters, which is based on boric acid. It can be sprinkled in carpets or swept into the gaps in your floorboards and acts to kill flea eggs and larvae. It will work similar to a flea bomb in helping to control the immature flea life stages.


Treatment of the outdoors is more complicated. Ideally all animals should be on flea control and stray cats should be kept away from your yard. Immature flea life stages are susceptible to the effects of drying, extreme heat and cold and direct sunlight. They love a humid, warm and preferably dark environment. Sweep up leaves, keep lawns short, limit the use of mulch, fence off areas of the yard that are warm and dark and protected from the elements (such as under the house or veranda and down the side of the house).

Salt (such as pool salt) can be sprinkled in some outdoor areas to act as a desiccant or drying agent to kill immature fleas. It can be irritating to your cat’s skin and is not great for plants, so you ultimately need to block off the area if you can. You can also use a yard spray to treat the area. Alternatively, there are also specialized pest companies that will treat your yard for fleas. Not all professional pest sprays treat fleas, and always make sure they are cat safe.


Make sure any pet beds can be washed in their entirety on a hot cycle in the washing machine (over 60ºC/140F for more than 10 minutes). It is not enough to just wash the cover of the bed as the fleas will burrow down into a mattress or foam. If your cat has access to an old couch outside as a bed consider what could be living in there, and get an easier to clean bed.

If your cat is fond of sleeping in the dirt or mulch or under a shady tree these can be great areas for a flea nest. Perhaps he is trying to keep cool and you could consider a nice cool bed instead. Sweep the dirt as much as possible to get rid of organic material such as mulch and leaves.


Sometimes in the hunt for a more ‘natural’ way to protect our pets, all sorts of weird and wonderful recommendations are made on the internet. Just because something is ‘natural’, that does not necessarily means it is safer. Dogs and cats are much different to humans and things that are safe for us (such as grapes, chocolate and paracetamol), can harm our pets. Registered flea products have years of research into safety and have very strict manufacturing controls. While natural remedies are often completely harmless, cats do have a tendency to ingest substances while grooming, so be wary of this when trying something new. In many ways a proven product is much safer than a ‘natural’ remedy posted on the internet with no research and safety data.

The best natural remedy for fleas in the environment is washing bedding on a hot cycle in the washing machine once a week and vacuuming every few days. Then tackle the yard and any other animals nearby, even if that means buying you neighbour some Advantage for her cats! The boric acid powders mentioned above are also great for killing fleas in the environment if you are reluctant to use a flea bomb. Also see the other environmental flea control options above.


Garlic is a common flea remedy and can be very toxic to cats, along with onions. Essential oils and in particular tea tree oil are very toxic if ingested, so are not pet safe. Tea tree is considered safe in animals if used at less than 1% concentration, but this is entirely ineffective for all its purported uses. We don’t tend to drink the contents of that scented oil infuser, but your pets will often groom themselves, so anything you spray on them has to be safe for ingestion. Citronella is particularly offensive to our pets, which is why it is used as a punishment in bark collars (don’t get me started on that one), so it seems particularly cruel to spray it all over them. Similarly lemon sprays are entirely useless as a flea repellent.

Fleas have adapted to be very clever parasites, so it is not just a matter treating your pet once a month. To really tackle those blood-suckers, you need to kill all those latent fleas in the environment to reduce re-infestation. We hope this article helped you find some solutions for your pets. If you have any other specific questions on how to treat your pet for fleas, please post a question in the Love That Pet forum. Sometimes with a little detective work a solution can be found that does not require large volumes of toxic chemicals to keep your pet comfortable this summer.


  • Flea medication can seems like it is not working because nothing kills fleas instantly
  • Treat the environment with flea bombs and regular vacuuming
  • Wash pet beds weekly on a hot cycle
  • Keep lawns short and yards swept
  • If you bathe your pet more than weekly flea products may not work
  • Treat all pets, even those free-roaming cats if you can!


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