Symptoms of Hypothyroidism in Dogs: Skin, Coat, Weight

The classic symptoms of hypothyroidism in a dog are weight gain without eating more, low energy and reluctance to exercise, hair loss on both sides of the body, a dull or thinning coat, flaky or greasy skin, darkened skin, seeking out warm spots, and skin or ear infections that keep coming back. Book a veterinary appointment if you are seeing these, because a blood panel is the only way to confirm a thyroid problem and because several more serious diseases look almost identical from the outside. If your dog is collapsing, seizing, breathing abnormally, unresponsive or cold and deteriorating fast, that is emergency care right now rather than a scheduled visit.

Hypothyroidism itself is usually a slow, grinding condition rather than a crisis. It develops over months, and most owners only connect the dots looking back at photographs. The rare exception is myxedema coma, a severe form in which a dog becomes profoundly weak, hypothermic and mentally dull, and that is a genuine emergency.

Why one missing hormone changes the whole dog

The thyroid gland sits in the neck and releases hormones that set the metabolic rate of nearly every cell in the body. When output drops, cells burn fuel more slowly. Hair follicles stay dormant instead of cycling into new growth. Skin turns over sluggishly and its barrier function weakens. Fat is cleared from the bloodstream less efficiently, which is why high cholesterol and triglycerides are common incidental findings on bloodwork in affected dogs. Heart rate slows. Heat production falls, so the dog feels the cold.

In dogs, the most common underlying causes are immune-mediated destruction of thyroid tissue, called lymphocytic thyroiditis, and idiopathic atrophy, where functional gland tissue is gradually replaced by fat. Both chip away at hormone output over a long period. That slow onset is the reason the symptom list is so scattered: nothing fails all at once, so the picture looks like a dog who is simply getting old.

It is typically a middle-aged to older dog problem, and it is seen more often in medium and large breeds. Golden Retrievers, Dobermans, Irish Setters, Boxers, Cocker Spaniels, Dachshunds and Airedale Terriers are among the breeds commonly described as predisposed. Breed and age raise suspicion, but they never confirm anything on their own.

Skin, coat and the ear infections that keep coming back

Skin changes are the reason most dogs end up in the exam room. The pattern is distinctive: hair loss that is roughly symmetrical on both sides of the body, usually sparing the head and legs, concentrated over the trunk, flanks, neck and tail. The tail can lose so much coat that it is described as a rat tail. The hair that remains often looks dry, brittle and faded, and regrowth after clipping is slow or does not happen at all. Crucially, this hair loss is usually not itchy on its own, which separates it from allergic skin disease.

The skin underneath may be dry and scaly, or greasy and strong smelling, and it often darkens into patches of grey or black pigment. Because barrier function and local immune defence are both affected, bacterial skin infections and yeast overgrowth become easy to acquire and hard to clear. A dog with recurrent ear infections or skin infections that return every time the medication stops is a dog worth testing for an underlying hormonal cause, rather than treating the same infection over and over.

The ear link is real and worth understanding. Hypothyroidism does not cause an ear infection directly. It changes the environment of the ear canal and the body's ability to police it, so ordinary bacteria and yeast get a foothold. Owners describe months of head shaking, brown discharge and smell, with each round of ear drops working and then wearing off. Treating the ear is still correct, and your vet will do that, but when the cycle keeps repeating, the question shifts to what is allowing it. Thyroid disease is one of several answers, alongside allergies and anatomy.

Weight gain, and the dogs who never gain a pound

The textbook presentation is weight gain despite no change, or even a reduction, in food. That is the signature worth noticing. A dog who eats the same bowl and steadily thickens through the waist and chest is telling you something about metabolic rate, not about willpower. Fat distribution tends to be general rather than the pot-bellied, thin-limbed shape more typical of other endocrine conditions.

But hypothyroidism without weight gain is common enough that a normal body condition score should never rule it out. Plenty of affected dogs stay lean, especially active dogs, working dogs and dogs on tightly controlled rations. In those dogs the coat, the energy level and the cold intolerance usually give it away first. Results vary from dog to dog, and no single sign is mandatory.

Appetite is a useful discriminator. Loss of appetite is not a typical feature of hypothyroidism. Most affected dogs eat normally or enthusiastically. A dog who is genuinely off food, losing weight, vomiting or looking unwell is pointing somewhere else, and that combination deserves prompt veterinary attention rather than a wait and see approach.

The face, the eyes and the look owners call tragic

In more advanced cases, a substance called mucin accumulates in the skin, thickening it and giving it a puffy, doughy quality that does not pit when pressed. On the face this produces drooping of the eyelids, thickened folds across the forehead and a heavy, downturned expression. Veterinary dermatology texts describe this as the tragic facial expression, and it is one of the few signs that is close to specific for the condition. Owners usually recognise it instantly in a side by side photograph taken a year apart.

Eye problems can appear too, though less commonly. Fat clearance from the bloodstream is impaired, and lipid can deposit in the cornea, producing a hazy, whitish ring or patch. Dry eye, with thick discharge and a dull corneal surface, has also been associated with thyroid disease. Facial nerve dysfunction can cause a drooping lip or an eyelid that does not blink properly on one side. Any change in the appearance of an eye, in vision, or in blinking should be examined, because corneal damage progresses quickly and eye problems have many causes unrelated to the thyroid.

Energy, behaviour and the seizure question

The behavioural picture is quiet rather than dramatic. Dogs sleep more, hesitate at stairs, lose interest in walks they used to demand, and seem mentally slower to respond. Owners frequently describe it as the dog ageing five years in one. Some dogs become withdrawn, and changes in anxiety, reactivity or irritability have been reported, though behaviour is influenced by so many factors that it is weak evidence in isolation.

Neuromuscular signs can occur in a minority of dogs: weakness, wobbliness, a head tilt from vestibular involvement, or dragging a paw. These overlap heavily with orthopaedic and neurological disease and need a proper examination to separate.

On seizures, be careful with what you read. A link between hypothyroidism and seizures in dogs is frequently discussed, but it is not a well established cause and effect relationship, and research suggests the association is far weaker than online discussion implies. Treating the thyroid is not a seizure plan. A first seizure, a cluster of seizures, or a seizure lasting more than a few minutes is an emergency, and the right response is immediate veterinary care, not a thyroid test ordered at home.

That is also the honest answer to what you will find searching owner forums. Reddit threads on hypothyroidism symptoms are genuinely useful for recognising patterns, especially the coat and energy descriptions that match your dog, and genuinely unreliable for diagnosis, dosing and interpreting numbers. Use them to decide to make an appointment, not to decide what is wrong.

Drinking, urinating, appetite, and how a vet confirms it

Increased thirst and frequent urination are not hallmark signs of hypothyroidism. When a dog is suddenly emptying the water bowl and asking to go out overnight, other conditions move to the front of the list, and that change deserves investigation on its own merits. The table below shows how the overlap tends to sort out.

Sign	Fits hypothyroidism	Also commonly caused by
Weight gain, normal appetite	Yes, classic	Overfeeding, reduced exercise, other endocrine disease
Symmetrical hair loss, no itch	Yes, classic	Other hormonal disease, follicular disorders
Recurrent ear or skin infection	Yes, as a background factor	Allergies, ear anatomy, parasites, yeast overgrowth
Lethargy and cold seeking	Yes	Heart disease, anaemia, pain, arthritis
Drinking and urinating more	Not typical	Diabetes, kidney disease, Cushing's, urinary infection
Loss of appetite, weight loss	Not typical	Many conditions, several of them serious
Seizures	Not an established cause	Epilepsy, toxins, metabolic and structural brain disease

Confirmation is a blood test, and it is more nuanced than one number. Vets typically look at total T4 alongside free T4 measured by equilibrium dialysis, canine TSH, and sometimes thyroglobulin autoantibodies, interpreted together with a full chemistry panel and the physical examination. The reason for the extra tests is that unrelated illness, and several common medications including steroids, phenobarbital and some sulfonamide antibiotics, can suppress thyroid values in a perfectly normal dog. That is called nonthyroidal illness syndrome, and it is the single biggest source of false diagnoses. Tell your vet every medication and supplement your dog receives before the blood draw.

Where a diagnosis is confirmed, management is lifelong oral thyroid hormone replacement, prescribed, adjusted and monitored by your vet with follow up bloodwork. Never set, change or stop that medication yourself.

Key Takeaways

• The core cluster is weight gain without eating more, low energy, symmetrical non-itchy hair loss, dull coat, flaky or darkened skin, cold intolerance and repeat skin or ear infections.
• Hypothyroidism without weight gain is common, so a lean dog is not excluded.
• Recurrent ear infections are a downstream effect, not a direct one, and persistent cycles justify looking for an underlying cause.
• Facial puffiness from mucin accumulation produces the drooping, heavy expression often called the tragic face.
• Increased thirst, frequent urination and loss of appetite point away from the thyroid and toward other conditions that need their own workup.
• The seizure association is weak and not established; seizures are an emergency regardless of thyroid status.
• Diagnosis requires a veterinary thyroid panel interpreted in context, because illness and medications can distort the results.

If this list sounds like your dog, write down what you have seen and when it started, bring older photographs, and talk to your vet. Your veterinarian owns the diagnosis, the testing and the treatment plan, and that is exactly where this belongs: the signs described here are shared by several conditions with very different consequences, and only an examination and bloodwork can tell them apart. Nothing you read online, including this page, substitutes for that appointment.

Related reading: Hypothyroidism in Dogs: Causes, Hypothyroidism in Dogs: Treatment, Dog Emergency Signs, and the full conditions library.