Peau et téguments

The integumentary system is the body's outer covering, made up of skin, coat, claws or hooves, and in some species feathers or scales. It acts as the first barrier against injury, infection, and fluid loss, while also playing a role in temperature regulation and, in many species, communication and camouflage. Because it is visible and easy to examine, integumentary problems are often the first sign owners notice that something is wrong, whether that is a bald patch, a limping cat with a swollen paw, or a bird pulling out its own feathers.

This system looks very different across the species UPC covers. Dogs and cats have fur-covered skin and claws; horses and cattle have haired skin and hooves; poultry and pet birds have feathers instead of fur; reptiles and fish have scales rather than either. Skin disease is also one of the more frustrating areas of veterinary medicine for owners, since many different underlying causes, from allergies to parasites to hormonal imbalance, can produce very similar-looking symptoms such as itching or hair loss.

Skin has two main layers: the epidermis, a thin outer layer that is constantly shed and replaced, and the dermis beneath it, which contains blood vessels, nerve endings, and the roots of hair follicles. Glands within the skin produce oils that help waterproof the coat and, in some species, produce scent used for communication. Hair grows in cycles of active growth and rest, which is why shedding patterns change with season in many dogs and cats.

Claws and hooves are both modified, hardened extensions of the skin built around the same basic structure, though they serve different purposes. A dog or cat's claw grows from tissue at the toe and is used for grip and defense, while a horse or cow's hoof is a much larger structure that bears the animal's full weight and grows continuously from a band of tissue at the top of the hoof wall. Both need regular trimming or wear to stay a healthy length and shape.

Birds have feathers instead of fur, which grow from follicles in the skin in a defined pattern and are replaced through periodic molting. Feathers serve insulation and flight, and their condition reflects overall health closely. Reptiles have skin made of scales that they shed periodically as they grow, and fish have scales embedded in a mucus-covered skin layer that protects against infection and helps them move efficiently through water.

Allergic skin disease is one of the most common integumentary problems in dogs and cats, triggered by environmental allergens, fleas, or certain foods, and it usually causes intense itching, redness, and secondary skin infections from repeated scratching. Parasites such as fleas, mites, and ticks affect the skin directly and are a frequent underlying cause of itching across nearly every species covered here, including reptiles and birds in the case of certain mite species.

Bacterial and fungal skin infections, including ringworm despite its name being a fungus rather than a worm, can develop on their own or as a complication of an already irritated skin barrier. Hormonal imbalances, particularly involving the thyroid or adrenal glands, often show up first as thinning coat, symmetric hair loss, or skin that becomes thin and slow to heal.

Species-specific problems are common too. Horses can develop laminitis, a painful condition where the tissue connecting the hoof wall to the underlying bone becomes inflamed, along with hoof cracks and thrush, a bacterial infection of the frog. Birds may pluck or chew their own feathers because of stress, boredom, or underlying illness. Reptiles can develop retained shed, where old skin fails to come off cleanly, and fish are prone to fungal patches and scale damage after injury or poor water quality.

• Allergic and parasitic skin disease in dogs and cats
• Bacterial and fungal skin infections
• Hormonal causes of coat and skin change
• Hoof, feather, and scale conditions specific to non-mammalian and hooved species

Persistent scratching, licking, or chewing at the skin is the most common sign of an integumentary problem, and it is worth noting exactly where on the body it happens, since the pattern often hints at the cause. Hair loss, whether in patches or spread evenly across the body, redness, scabs, or a greasy or unusually smelly coat are all worth mentioning at a vet visit even if the pet does not seem especially bothered by them.

In birds, watch for feathers that look chewed or frayed, bald patches especially on the chest, or a bird that plucks feathers from itself repeatedly. Reptiles showing patchy, incomplete shedding, or areas of skin that look discolored or infected, should be evaluated, since retained shed can restrict circulation to a toe or tail tip if left alone. Fish with fuzzy white or gray patches on the skin, frayed fins, or scales that look raised rather than lying flat may have a fungal or bacterial skin problem.

For horses and cattle, watch for cracked, crumbling, or unusually hot hooves, a reluctance to move that improves once weight comes off the affected foot, or a strong odor from the hoof that can indicate thrush. Claws that are overgrown, split, or bleeding at the base in dogs and cats also warrant attention, as do any new lumps or masses found while petting or grooming.

A hoof that is hot to the touch, especially alongside reluctance to move or a strong digital pulse a vet or experienced handler can check, needs emergency attention, since laminitis progresses quickly and early treatment considerably improves the outcome. Sudden, widespread hair loss with visible skin damage, or a wound that is deep, actively bleeding, or clearly infected, also needs prompt same-day care.

Same-day or next-day veterinary attention is reasonable for a skin infection that is spreading, intense itching that is disrupting sleep or causing self-trauma, or a bird that has plucked a significant area of feathers in a short time. A reptile with retained shed around a toe or tail tip should also be seen promptly, since restricted circulation there can lead to tissue loss.

A routine appointment is enough for mild, longstanding itching without dramatic skin changes, gradual coat thinning in an older pet, or overgrown claws that simply need trimming. Recurrent skin infections, even mild ones, are worth investigating at a routine visit too, since they often point to an underlying allergy or hormonal condition that benefits from a proper diagnosis rather than repeated short-term treatment.

Why does my dog keep getting skin infections even after treatment?

Repeated skin infections are usually a symptom of an underlying problem such as allergies or a hormonal imbalance, rather than a stand-alone issue. Treating the infection each time it appears without addressing the underlying cause tends to lead to it coming back.

Is it normal for my bird to lose some feathers?

Regular molting, where feathers are shed and replaced in a normal pattern, is completely normal and usually not concerning. Feather plucking, where a bird actively pulls out its own feathers, particularly on the chest or legs, is different and usually indicates stress, boredom, or an underlying medical problem.

What is laminitis and why is it so serious in horses?

Laminitis is inflammation of the sensitive tissue connecting the hoof wall to the coffin bone inside it, and in severe cases the bone can rotate or sink within the hoof. Because this tissue supports the horse's entire weight, laminitis can cause severe pain and, in advanced cases, permanent lameness.

My cat is losing hair in patches. Is that always allergies?

Not always. Patchy hair loss can come from allergies, but also from parasites, fungal infection, hormonal disease, or even overgrooming caused by stress or pain elsewhere in the body, so a vet exam is usually needed to narrow down the cause.

How often should I trim my dog's nails?

Most dogs need a nail trim every three to four weeks, though this varies with how much natural wear they get from walking on hard surfaces. Nails that are long enough to click on the floor or that curl back toward the paw are overdue for a trim.