Why does my dog keep scratching? Six common causes, and when to see the vet

Reading time 5 min · Level 1: Why the symptom appears

The short answer: Every dog scratches now and then. It starts to mean something when scratching becomes a pattern: every evening, after every walk, for more than a couple of weeks in a row. The most common causes are parasites, an allergy to something in the environment, an allergy to something in the food, dry or over-washed skin, and infections that take hold in skin that is already irritated. Where on the body the dog scratches often tells you more than how much. And if the scratching causes sores, bald patches or redness, it is a matter for the vet, not for a jar.

Why itching is so common

The skin is the dog's largest organ and the one that meets everything: grass, mites, pollen, shampoo, fleas and whatever is in the food bowl. Roughly one in five vet visits for dogs and cats is about itching¹. Agria, the Swedish pet insurer that sees the pattern in its claims data, sums up the causes in three groups: parasites, allergies, and inflammation or infection in the skin². The three are also connected. An allergic dog scratches its skin open, bacteria and yeast take hold, and the itch gets worse from the infection than from whatever started it.

Six common causes

1. Parasites. Fleas, lice, mites and sarcoptic mange. Fleas are the most common, and the itch often sits at the base of the tail, on the belly and on the thighs. A dog that is allergic to flea saliva can scratch intensely from a single bite without you finding a single flea. Sarcoptic mange causes a violent itch that often starts on the elbows, ear edges and hocks, and can spread to other dogs in the household. Parasites are the first thing the vet rules out, because they are both common and easy to treat.

2. An allergy to something in the environment. Known as atopic dermatitis, or atopy. The dog reacts to mites, pollen or mould, and the itch typically sits on the paws, in the ears, in the armpits and on the belly. It usually starts before the dog turns three, often returns seasonally at first and becomes year-round over time³. Some breeds are over-represented, among them the West Highland white terrier, French bulldog, Labrador and golden retriever. Atopy cannot be cured but can be kept in check, and it is a diagnosis the vet reaches by ruling out everything else first⁴.

3. An allergy to something in the food. Less common than many think, but it exists. When researchers reviewed published cases of food allergy in dogs, the most common triggers were beef, dairy, chicken and wheat⁵. In other words, what the dog has eaten most, not the latest new thing. Food allergy often causes itching all year round, sometimes together with loose stools or recurring ear infections. The only way to know is a strict elimination diet for six to eight weeks under the vet's guidance. Blood and hair tests for food allergy have not proved reliable.

4. Dry skin and too much washing. Dry indoor air in winter, washing with the wrong shampoo or too often, and a food low in fatty acids can all give a dull, flaky skin that itches. This is the cause you can most often do something about yourself.

5. Skin infections. Bacteria and yeast (Malassezia) thrive in warm, moist and already irritated skin: skin folds, between the toes, in the ears. They are rarely the root cause but often what makes the itch unbearable. Odour, greasy skin and darkened patches are typical signs. Infections need treatment, not just a milder shampoo.

6. Stress and boredom. Some dogs lick and chew their paws for the same reason people bite their nails. It is a diagnosis of exclusion. Before you land there, the five points above should be ruled out.

When to see the vet

Straight away if the dog scratches itself into sores, bald patches or redness, if the ears smell or are red, if several dogs in the household are itching at the same time, or if it is a puppy. Within a couple of weeks if the itch does not ease even though you have changed shampoo and ruled out parasites. Itching is distressing for the dog, and the longer it goes on, the more skin is damaged and the more infections get a chance to set in. Bring a list of food, treats and supplements. It saves time for both of you.

What you can do yourself in the meantime

Rule out fleas and ticks. Comb through the coat over a sheet of white paper. Black specks that turn reddish brown when wet are flea droppings. If you find anything, or are unsure, treat according to your vet's advice.

Wash properly, not often. A mild dog shampoo made for sensitive skin, lukewarm water, rinse thoroughly and dry completely. Moisture left in the coat favours yeast. Human shampoo has the wrong pH for dog skin and makes things worse.

Look at the fatty acids. Omega-3 fatty acids are one of the few supplements with support in studies for allergic skin, as a complement that can reduce the itch somewhat and let the dog manage with less of other treatment. Allow around two months before you see an effect⁴.

Change one thing at a time. If you switch food, switch shampoo and start a supplement in the same week, you will never know what helped. Note where the dog scratches and how often, so you have something to show the vet.

That was the short answer. If you have a question about your own animal, email us. We reply within 24 hours.