Why does my dog have fleas in autumn?

The short answer

Fleas surge indoors in autumn because turning on your central heating can wake up dormant flea pupae that have been lying in your carpets and your dog's bedding since summer. They hatch once your home warms up, so your pet might start scratching just as the weather turns cold!

Why do dog fleas get worse in autumn?

The outdoor flea season winds down through October and November as temperatures drop. But indoors is another story - it’s where the autumn flea surge happens.

Adult fleas lay their eggs during the summer, which can fall off your dog and settle into carpets, rugs, sofas and bedding. Lots of them grow into pupae - a tough, cocoon-like stage. Then, they wait.

That's why so many owners see their first flea problem of the year in autumn or early winter. The moment the central heating comes on, those conditions are perfect for dormant fleas to hatch! 

Why does central heating bring fleas out?

Fleas love warm, damp air. Their sweet spot is around 21°C to 29°C, which is about the temperature of a nicely heated living room. The fleas didn’t arrive with the cold - they’ve been in the house all along.

Pupae can stay dormant for weeks or even months. They’re tough enough to sit out the cold until something tells them it’s time. Warmth does exactly that. Switch the heating on, and you just might wake up a whole batch! That’s why a flea problem can seem to appear overnight.

Where do most fleas hide?

Here’s a surprising (if slightly gross) fact. Any fleas you might spot on your dog are just a small part of the problem. Around 95% of fleas in your home are already living there as eggs, larvae and pupae, tucked into floors and soft furnishings!

It's a numbers game. A female flea can lay up to around 50 eggs a day, and those eggs will end up wherever your dog goes - their bed, the car, the sofa… 

That’s why using a flea treatment on your dog rarely solves the problem on its own. If you don’t sort the house too, the next wave is already waiting in the carpet!

How do I know if my dog has fleas?

Scratching in autumn is worth taking seriously. Look out for these signs of fleas on dogs:

• Scratching, biting or nibbling more than usual - often around the base of the tail, the belly and the hindquarters

• Flea dirt - tiny black specks in the coat or bedding that turn reddish-brown on a damp piece of tissue

• Red, sore or scabby skin - or thinning fur and bald patches where they’ve scratched too much

• Live fleas - these tiny, dark brown insects are easiest to spot with a flea comb over a white surface

• Restlessness - or any signs of an unsettled, itchy dog

Some dogs are allergic to flea bites (flea allergy dermatitis) and for them even one bite can cause a big reaction. If you suspect your dog might have fleas, it’s best to act early. Fleas are easily treatable, but your home needs care too:

• wash fabrics and any bedding, blankets or sofa cushions your pet has used on a hot cycle

• vacuum carpets, rugs, stairs, skirting boards, and upholstered furniture daily for at least 7 days, making sure to empty the canister or vacuum bag into an outdoor bin after each use

• apply a house flea spray or treatment

Focus on the warm, sheltered spots fleas love. That could be under furniture, along skirting boards and wherever your dog sleeps. Keeping these prevention methods going through the colder months will help to catch any infestations early and keep your pets and home clean and flea-free.

Dog flea treatment FAQs

Why does my dog have fleas in winter?

It’s because a heated home means fleas are active all year. Eggs and pupae that settled into your carpets over summer carry on hatching indoors, so fleas don’t switch off when it gets cold. They just wait for things to warm up!

What should I use to treat my dog?

Your vet is the best person to answer that. There are lots of flea products out there, and the right one depends on your dog’s size, age, health and lifestyle. 

Can I use a dog flea treatment on a cat?

No, you should never use a dog flea treatment on cats. That’s because some dog treatments contain permethrin, which is toxic to cats and can be fatal. If you’ve got both pets in the house, call your vet first to discuss the best way to de-flea.

Do dogs still need flea treatment in winter?

Yes. A big mistake many owners make is treating their pets during the summer, then stopping in autumn as the weather cools off - just as indoor flea season gets going! A heated home keeps fleas active all year, so year-round prevention will help keep them out.

When should I take my dog to the vet?

Call your vet immediately if your dog is scratching until their skin is raw, they’re losing fur, or they have broken or infected-looking skin. It's also worth a check-up if you spot signs of a flea allergy, or you're not sure the treatment you're using is right.