What this means
The first thing worth separating is general moulting from local balding. In a moult, hair comes out evenly over the whole body, the skin stays healthy, and the dog is not scratching. If round or irregular bald patches appear, or the coat thins specifically over the flanks, belly or tail, that is a different picture.
The second useful distinction is whether your dog is itchy. Hair lost because of itching comes out because the dog chews and rubs it away. The itch is then the primary problem and the baldness is the consequence. Hair that falls with no itching at all more often leads towards hormones or changes in the hair follicle.
Symmetry is worth noticing too. Coat thinning equally on both sides of the body, over both flanks for instance, points more towards an internal, hormonal cause. Irregularly scattered bald patches of differing sizes, with scale or crusting, point more towards a skin disease or parasites.
Finally, look at the skin under the coat. Redness, flaking, darkened or thickened skin, spots and smell tell your vet far more than the amount of hair on the carpet.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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Seasonal moulting
In spring and autumn hair comes out evenly across the body while the skin stays healthy. Grooming helps and no bald patches appear.
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Itching and self-chewing
Allergy or parasites cause itching and the dog removes the coat itself. The pattern is bald areas exactly where teeth or paws can reach.
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Skin mites
Some mites damage the hair follicles and cause bald patches, frequently around the eyes and on the paws. It turns up more in young dogs.
About the condition: Demodectic mange -
Skin infection
Bacteria or yeast cause round bald areas with scale, redness and smell. Infection often settles onto skin that was already damaged.
About the condition: Skin infections -
Too little thyroid hormone
When the thyroid makes too little, the coat thins symmetrically, the skin thickens, weight goes on more easily and the dog becomes less active.
About the condition: Hypothyroidism -
Too much hormone from the adrenal glands
An excess causes thinning over the flanks, a rounder belly, and increased thirst and appetite. The changes build over months.
About the condition: Cushing's disease
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Whether the coat thins evenly, or there are distinct bald patches
- Whether the balding is symmetrical on both sides
- Whether your dog is scratching and chewing
- What the skin underneath looks like: red, flaking, darkened
- Whether weight, thirst or energy have changed
- Whether the skin has started to smell
When to book a routine visit
Book a visit if bald patches appear, if the coat thins symmetrically on both sides, if the skin is red, flaking, darkened or smelly, or if weight, thirst and energy have changed alongside it.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Hypothyroidism Hormones and metabolism Hypothyroidism is a condition in which the thyroid gland produces too little of the hormones that regulate metabolism. Because these hormones affect almost the whole body, a shortage gradually slows many of its processes. The changes come on slowly, so they are easy to mistake for ageing or simple laziness.
- Allergies (food, skin and environmental) Skin and coat An allergy is an overreaction of the immune system to substances that are essentially harmless, such as pollen, house dust mites, moulds, flea saliva or an ingredient in food. In dogs it shows up mainly in the skin and ears, and constant itching wears a dog down and can open the way to skin infections. More than one trigger can be involved at once, so finding the cause takes patience.
- Demodectic mange Skin and coat Demodectic mange is a skin disease caused by microscopic Demodex mites that live in the hair follicles. A small number of them live on healthy dogs too, but when the immune system fails to keep them in check, the mites multiply rapidly and damage the skin and coat. It can stay small and local or spread over the whole body, which is a sign that the dog's body is struggling to cope.
- Alopecia X (black skin disease) Skin and coat Alopecia X is a condition in which the hair growth cycle is disrupted: the coat gradually thins until bald patches appear on the body and the exposed skin darkens. It neither hurts nor itches, so it affects the dog's looks more than its wellbeing. Hormonal disorders can look very similar, though, so changes in a balding dog's coat are worth showing to a vet.
- Sebaceous adenitis Skin and coat Sebaceous adenitis is a skin disease in which inflammation damages and over time destroys the sebaceous glands, which make the oils that protect the skin and coat. Without this protective layer the skin dries out and flakes, the hair breaks and falls out, and the skin becomes more prone to infection. The disease is thought to be inherited and is long-lasting, and what lies behind particular skin changes is for a vet to work out.
- Cushing's disease Hormones and metabolism Cushing's disease is a condition in which the body makes too much of a stress hormone. This hormone affects many of the body's processes, so an excess gradually changes a dog's appetite, skin, coat and muscles. The changes come on slowly, so they are easy to mistake for simple ageing.
- Skin infections Skin and coat Skin infections are caused by bacteria or yeast that start to multiply when the skin's defences are weakened, for example by an allergy, parasites, moisture trapped in skin folds or constant scratching. An infection can stay on the surface or reach the deeper layers of the skin, causing pain and intense itching. What caused the infection and what keeps it going is for a vet to work out.
- Fleas Parasites Fleas are small, jumping parasites that feed on a dog's blood and cause itching. Some of them live on the dog, while the eggs, larvae and pupae live in the home: in the dog's bed, carpets and soft furnishings. That is why fleas can keep coming back even when none are left to see on the dog; your vet can advise on protecting your dog and your home.
Body systems: Hormones and metabolism Skin and coat Parasites