Gemma Gaitskell
Dr Gemma Gaitskell (BVetMed MSc MRCVS, Royal Veterinary College, London)
Flea Prevention

Fleas are an extremely common type of non-flying parasite that are found around the world which can affect all sorts of animals. They feed on blood and can also infect the environment.

Here we take a look specifically at the dog flea and its life cycle and how dogs are affected, as well as treatment and prevention options.

About Fleas and Their Life Cycle

Flea Life Cycle

There are many different types of fleas, they are all very similar in structure and appearance but specific to the species which they prefer to feed on. Fleas are small insects with a laterally flattened body, which helps to allow them to move more easily between hairs and they measure 1-6mm in length. Fleas do not fly but actually jump onto animals. In order to survive, fleas must feed on blood from an animal with female fleas being larger than males.

It takes 3-4 weeks in warm conditions, for example in the UK summertime, for a flea egg to hatch and become an adult flea. This time frame is affected by temperature and, in colder conditions, can be considerably longer. Once a flea is on a dog it is usually quick to feed on its blood and lives between 7-10 days. Flea droppings or dirt appear like small dark grains of earth or dirt on the dog.

Flea Eggs

Female fleas lay eggs, which are oval shaped and ivory in colour, which then fall off the dog onto the floor – often in places where the dog moves quickly, scratches or shakes.

Flea Larvae

The next stage in the flea’s life cycle is the larval stage. Larvae are small –around 2-5mm – and white to yellowish in colour with a maggot like appearance. Flea larvae do not like light, so migrate to darker areas, for example under furniture or into carpets.

Flea Pupae

The larvae then pupate into pupae, which are surrounded by a cocoon, which is tacky to touch, picking up small bits of dirt and dust from the environment, which act as camouflage. The time the adult flea takes to emerge from the cocoon is dependent on the environmental temperature and humidity. The warmer the temperature the faster they will leave the cocoon.

Adult Fleas

Fleas can survive for a number of days in the environment before feeding, but once they have fed from an animal they can only survive a relatively short time of approximately few hours before needing to feed again.

The environment in which a dog lives can greatly affect the risk it is at of getting fleas. If a dog lives largely indoors and there are no other pets in the household or nearby, it is at a relatively low risk. The amount of risk related to the environment and the level of sensitivity of a particular dog to flea bites will dictate how strict flea control needs to be.

Problems Caused by Fleas

Closeup of Adult Dog Flea

Closeup of Adult Dog Flea (Luis Fernández García /

Although diseases that fleas transmit are less well-publicised and rarer than those transmitted by other parasites, such as ticks, there are still some diseases that can be carried and transmitted by fleas to humans, so if dogs are living in a house, it is particularly important that there is some kind of flea control program in place. Apart from transmitting various diseases fleas can also cause more immediate problems to the dog they are feeding from.

Flea Allergic Dermatitis

Flea Allergic Dermatitis is an extremely common condition caused by fleas. When fleas feed on a dogs blood, their bite and saliva cause irritation to the skin and aggravation. If a dog is prone to flea allergic dermatitis, their saliva causes hypersensitivity and this results in inflammation. Some breeds of dogs, especially those prone to skin problems and allergies, can be more susceptible to suffering from flea allergic dermatitis, but any dog can be affected. This condition is most likely to be seen in puppies over 6 months of age and dogs between 3-6 years old – although dogs of any age can suffer from it.

The irritation caused by flea bites cause dogs to bite, chew, lick and scratch the area where they were bitten, and this in itself can lead to secondary problems and skin infections. The level of irritation is usually related to the number of bites and fleas on the animal, but if a dog does suffer from flea allergic dermatitis, even a single flea bite can cause significant irritation. Other conditions that can cause similar clinical signs are other allergies to foods or the environment and various different kinds of mites.

Detecting Fleas

Sometimes detecting fleas can be difficult as they can be hard to find. They move quickly and away from light and are also harder to see on dogs with dark hair and skin. However, a combination of clinical signs and evidence of flea dirt can also be used to diagnose whether a dog has fleas. Combing hair, with a fine tooth comb onto a moist piece of white paper can help establish if flea dirt is present.

How to Prevent and Treat Fleas

Dog Flea Collar

Preventing fleas and, therefore any diseases which they cause and transmit, revolves around effective flea control and removing any flea populations from the dog itself and the dogs’ environment. Understanding the flea’s life cycle and which stages are susceptible to different chemicals is key to this. This means that the two principal method for controlling fleas revolve around killing adult fleas which may be living on a dog and also tackling any eggs or fleas which haven’t fed which may be inhabiting in the environment.

Chemical Treatments

The most efficient and effective method of killing fleas is by using chemicals. The chemicals which are used for flea control in dogs have been tested extensively and have been shown to be safe in the dog, as well as effective at killing fleas. There are numerous products which can be found under different brand names for flea control, but the active ingredient which they contain is what makes them effective against fleas. Some of the most common chemicals and combinations which are effective at controlling fleas include:

  • Fipronil
  • Fipronil and (S)-methoprene
  • Imidacloprid
  • Imidacloprid and permethrin
  • Imidacloprid and moxidectin
  • Indoxacarb
  • Indoxacarb and permethrin
  • Pyriprole
  • Metaflumizone and amitraz
  • Selemectin

Application of Topical Flea Treatments

All flea control products come with instructions on how often they should be applied and the best way to do this, as well as how effective they are against different stages of the flea life cycle. It is also important to consult from what age the product can be applied as some are not appropriate for very young puppies. The most common products are found either in the form of a collar, tablets for oral administration or ‘spot-on’ type drops which are applied to the dog at the base of the neck in between the shoulder blades. It is important that dogs are not able to reach the area where a product is applied and lick it off.

The choice of which product to use is determined by what most suits the dog and owner’s lifestyle. Efficacy of some products is affected by water and dogs should not be bathed for a number of days before or after they are applied. Dogs which swim on a regular basis may also need more frequent applications of flea treatments.

Oral Flea Treatments

There are also some flea control agents which can be administered orally, usually these are given with food to make administration easy and these can have good levels of efficacy. Some of the active ingredients which these products may contain include:

  • Spinosad
  • Spinosad and milbemycin oxime
  • Nitenpyram
  • Lufenuron
  • Lufenuron and milbemycin oxime
  • Afoxolaner

Sometimes dogs will already be suffering from severe irritation and itching and skin infections before flea control is implemented. If this is the case it may also be necessary to treat the symptoms which are already present to provide the dog with relief from any irritation and itching. If there are numerous pets in a household all of them should be treated at the same time, and periodically with an effective treatment.

Environmental Flea Control

Products which are most effective at controlling fleas in the environment contain different chemicals, these act by disrupting flea development and killing eggs. Some examples of chemicals found in products which are effective for environmental flea control include:

  • Methoprene
  • Pyriproxifen
  • Lufenuron
  • Cyromazine

If there is flea infestation a combination of treatments on the dog and environmental measures should be used for maximum effect. To properly get a flea infestation under control, it is also important that control measures are maintained for a sufficient period of time to ensure that all life-stages which may be in the environment are eliminated.

In addition to the use of chemicals thorough cleaning of any areas where fleas may be concentrating in the environment, such as carpets and under furniture may help. Hoovering and cleaning carpets, as well as moving furniture can be used as an additional measure when applying chemicals designed for environmental control.

Consulting Your Local Veterinarian

Products for flea control are available from many different sources but it is always advisable to consult a veterinarian as to which is most appropriate for your dog and its lifestyle. Products sold and prescribed through a vet will be guaranteed to be effective and safe for your dog. Many products which are used to control fleas are also effective against other parasites and, if a dog has already been treated with another chemical, it is important to establish that the combination won’t cause any side effects.

If any additional treatment is necessary to relieve itching or treat infections your vet will also be able to provide advice. If there are cats in a household care should be taken if using any products containing permethrin, as this chemical can be toxic to cats.

Some breeds of dog, such as Border Collies, can be sensitive to certain chemicals contained in flea and parasite control products, so it is important to consult your veterinarian as to which is most suitable and take care when using combinations of chemicals contained in the same product.

The Importance of Flea Prevention

Fleas are a very common problem in dogs and flea allergic dermatitis is one of the most common diseases that dogs can suffer from. As fleas can be found in the environment, it is very likely that nearly all dogs will carry or be bitten by a flea at some point in their lives. Whether this then becomes a problem and leads to infestation is dependent on the type of environment the dog lives in and how strict and effective flea control measures are.

The key to effective flea control is consistent use and selection of an adequate flea control product which is appropriate for an individual dog’s lifestyle. Dog fleas can bite people and flea infestation in houses can be difficult to treat, so it is always recommended to use preventative methods rather than to wait for a dog to become infested with fleas.