Dogs love a good scratch. But if your pup’s itchiness seems to be more than just a satisfying scratch, it could indicate a problem. Today we will discuss the various reasons why your dog might be itchy, and what we can do to prevent it.

Normal Itching

Just like humans, dogs have itch receptors on their skin that respond to a variety of stimuli, causing an itchy sensation in the skin that makes them want to scratch! Itchiness is termed ‘pruritus’. Physical touch, heat, chemicals and even electrical activity can all stimulate itch receptors. Some receptors also respond to the body releasing histamine (the same chemical that causes allergic reactions). 

Any minor stimulus can cause a little itch that dogs have to scratch. And as long as these scratching sessions are short, mild and infrequent, there is unlikely to be a problem. However, if your dog’s itchiness is starting to concern you, there may be an underlying cause worth investigating.

If itching becomes a habit or severe, the skin can become damaged. This causes pain, inflammation and further discomfort that many dogs will sooth with more scratching, creating a vicious spiral. Damaging the skin’s protective barriers also allows bacteria and fungi to colonise, leading to skin infections. Severe trauma from itching can even lead to long-lasting damage.

Parasites

Parasites are an incredibly common cause of itching in dogs, particularly young puppies, dogs that spend a lot of time outdoors, and those not regularly treated with anti-parasitic medications.

Fleas top our list; these little insects love to jump onto your dog and bite to feed

This results in the irritation, itching and prolonged scratching fleas are known for. As well as pruritus, fleas can transmit diseases such as tapeworms. With very heavy infestations, the fleas can drain so much blood they cause anaemia. Some dogs are even hypersensitive to flea bites and will itch uncontrollably at the slightest touch (more on this later). Eradicating fleas is tricky, and needs thorough treatment of all animals and the environment. The hardy eggs and pupae of fleas are very hard to kill, so full extermination can take months. It is also important to remember that thanks to the invention of central heating, there isn’t really a ‘flea season’ anymore, and dogs can catch fleas at any time of year. 

Mites are a group of arachnids that cause pruritus (itching), particularly in young dogs 

The most common in dogs include Cheyletiella, Otodectes, Trombicula, Sarcoptes and Demodex. Infections vary from mild irritation from Cheyletiella to severe itching and redness with Sarcoptes. The ear mite, Otodectes, commonly causes itchy ears and a build up of wax in young puppies. Demodex is often localised to the paws, ears and skin around the eyes, but can be seen all over the body, but is usually only a problem in elderly animals or those with compromised immune systems. Trombicula, or harvest mites, are little orange mites that can just be seen with the naked eye – as the name suggests, they are especially common in Summer and Autumn. A good veterinary-prescribed drug is usually enough to kill these critters. 

Ticks are blood-sucking parasites 

They seem to be more common in some parts of the country than others – dogs that love hiking and running in long grass are especially at risk. Their bites can cause some localised irritation and scratching, but the biggest risk is the spread of tick-borne diseases such as Lyme disease and Babesia. These diseases can cause significant illness in dogs, and can also affect humans too. Identifying and removing ticks quickly is critical, so always check your dog for ticks after walking near tick habitats. 

Lice can be a problem sometimes

Small chewing or blood-sucking insects, laying eggs as nites – we’re sure you’ve come across them in one species or another! However, in dogs, they rarely cause problems for a healthy host.

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Finally we have hookworms

These curious little roundworms are common in puppies kept in very poor conditions, such as at puppy farms. As well as the traditional faecal-oral route like most roundworms, hookworms can also infect puppies by burrowing through their skin, commonly in the paws. This results in itchy, sore and swollen paws. The worms migrate to the intestines to reproduce, also causing diarrhoea, before eggs are passed out in the faeces to hatch and begin the cycle again. Good hygiene and regular worming are important to prevent these worms causing pruritus.

Bacteria and Fungi 

Normal dog skin is covered in bacteria and fungi – many are commensals that live there and provide a benefit, such as outcompeting pathogenic organisms. This is called the skin microbiome. Skin is usually resistant to microbes but if the skin becomes damaged, both commensal and pathogenic bacteria and yeasts can colonise and cause infection. Most infections are secondary, infections arising as a result of a primary disease. This means that parasites, allergies and hypersensitivities, autoimmune disease, and other diseases causing pruritus can result in secondary microbial infection, worsening the itchy sensation. 

Bacterial infections can present in a number of ways. Superficial infections (pyoderma) can look like little whiteheads or wetness on the skin. Deep pyoderma can cause the skin to become thickened, hairless and with deep infection tracts. Deep pyoderma can be difficult to treat. In both cases, antibiotics are needed, as well as treatment of the primary cause. 

Yeast infections, particularly of the commensal Malassezia, are a common consequence of skin damage. These kinds of infections tend to cause greasy smelly skin and are often very itchy. It is common to get yeast infections in the ears, skin folds and between the paws, though they can happen anywhere. Treatment involves local and systemic antifungals.

Ringworm is a specific group of fungi that colonises the living hair of animals, including humans. It often causes characteristic ring-shaped lesions on the skin, hence the name, though it can look like any shape. The infection tends to cause hair loss as the fungi kill the hair they reside in. Ringworm can infect humans, so people should be careful if their pets have it. Treatment can be difficult, and may involve topical or systemic antifungal drugs, antiseptic washes and strict environmental control.

Allergies 

Allergies are where the body responds to a normal substance (termed an allergen) with an exaggerated response, by releasing inflammatory chemicals like histamine. This means that a dog with allergies becomes very itchy when coming into contact with a substance that a non-allergic dog would not react to. In many cases, the dog appears to have a genetic predisposition to developing (often multiple) allergies – we term this atopy

Many things can be allergens. Substances that cause a direct reaction on the skin cause contact or environmental allergic reactions. Substances that must be ingested cause food allergies. Even fleas can cause an extreme reaction – we call this flea allergic dermatitis. Certain breeds are more predisposed to allergies than others, such as West Highland White Terriers, German Shepherds, Boxers, and French bulldogs. Allergies tend to start around a year of age. 

It can be difficult to diagnose allergies, but early warning signs can be recurrent ear infections, red eyes, diarrhoea and, of course, lots of itching. Definitive diagnosis can be performed via skin testing, but this can be expensive. Treatment is also complicated – it is difficult to ‘cure’ allergies, so management is generally preferred. This may involve anti-inflammatories or anti-allergy tablets, regular anti-allergy injections, or immunotherapy. If the allergies are diet-related, exclusion diets or hypoallergenic hydrolysed diets can reduce flare-ups.

Other Skin Diseases

There are some rarer skin diseases that can also cause pruritus. One category includes autoimmune diseases. This is where the body’s immune system starts to attack its own cells in some way. Pemphigus foliaceus is a condition where the body attacks the skin cells’ connective proteins, resulting in the skin peeling and blistering away. Pemphigus vulgaris is a similar disease but tends to be localised to mucocutaneous junctions, such as the mouth, nose and feet. Lupus is a condition where the skin is hypersensitive to light, and is easily damaged. It results in inflammation, pruritus, loss of skin colour and ulceration. It is most common on the nose.  All of these conditions can be managed with anti-inflammatories and immunosuppressants. 

Finally, there are certain skin cancers that result in pruritus. Two of the most common in dogs are mast cell tumours and cutaneous lymphoma. Mast cell tumours are malignant tumours that often release inflammatory chemicals like histamine. This results in local inflammation and itchiness. Mast cell tumours can wax and wane in size, and almost anything can look like a mast cell tumour. Treatment is done either by careful surgical removal or chemotherapy drugs. Similarly, cutaneous lymphoma is a malignant tumour that causes pruritus, crusting, ulceration and hair loss. They can originate in the skin or spread from other areas, and are treated in similar ways to mast cell tumours. 

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Summary

As you can see, there is a huge list of possible causes of itchiness in your dogs, and the list is by no means exhaustive. It is important to remember that common things are common, and that parasites and allergies are by far the most common cause of excessive itchiness in dogs, especially younger ones. Don’t panic that every scratch is a serious autoimmune disease or cancer! Nevertheless, it is always important if your dog is chronically itching to speak to your vet before they start to damage their skin and cause further issues like infections. With some help from your vet, you can ensure your dog is comfy and happy.

Further Reading