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A variety of skin problems can affect dogs and cats, including allergies, bacterial and fungal infections, and parasite infestations. Most skin problems in pets are curable or manageable, so if your pet seems itchy or has skin that doesn't look healthy, contact your vet. It is important to have your vet examine your pet to determine the cause of the problem.
What are the causes of skin disease?
A wide variety of skin and coat conditions can cause your pet to itch and scratch, but pinpointing the problem can sometimes be difficult because many skin problems can be very similar. Also, pets may have more than one disorder at the same time, or may have allergic reactions that affect the ears, eyes, GI tract, or respiratory tract (eg asthma) as well as the skin, which can complicate the diagnosis. There are four major categories of skin conditions seen in cats and dogs:
Allergic skin diseases
Allergic skin disease develops when your pet's immune system overreacts to certain substances (allergens), causing clinical signs that affect the skin. Allergens may come from the environment, such as mould, dust mites, or plant pollen, from parasites, or even from food. Your pet may come into contact with these allergens in several ways:
- Direct contact with skin. Allergens that are absorbed through the skin, eg chemicals, plant materials, drugs, or natural or artificial materials, cause a condition called atopic disease. When it is associated with just skin disease it is called atopic dermatitis. Direct contact is the most common route of allergen exposure in allergic skin disease.
- Breathing. This is a less common exposure route than direct contact, but inhaled allergens can also cause atopic disease or atopic dermatitis.
- Insect bites. Pets that are allergic to insect bites can develop skin disease. Flea allergy is the most common example. Components of flea saliva can cause flea allergy dermatitis in sensitive animals when they are bitten by fleas.
- Eating. Some cases of allergic skin disease in pets are triggered by an allergy to a protein in the pet's food or treats. Some pets have atopic dermatitis caused by both food and environmental allergens. Food allergens can also cause food allergy (food hypersensitivity), which often causes vomiting and diarrhoea as well as skin problems.
Allergic skin disease causes itching, and pets that scratch excessively can damage their skin. Sometimes, frequent chewing, scratching, and biting can cause secondary skin infections, wounds, scabs, hair loss, and other problems.
Diagnosing allergic skin disease can be challenging because different types of allergies can have the same clinical signs, and allergic skin disease can look like many other types of skin problems. Your vet will try to rule out other types of skin irritation before making a diagnosis of allergic skin disease.
Ideally, treatment of allergic skin disease involves reducing or eliminating your pet's exposure to the allergens that are causing the problem. If a pet has a food allergy, a special diet may be prescribed. If your pet is allergic to fleas, safe and effective flea control is essential to controlling the problem. For pets that are allergic to environmental allergens, such as grass or house dust, limiting their exposure to the allergens can be helpful, but this is often difficult, and medications are often necessary. In some cases, allergy testing may be recommended. If the exact allergens that the pet is sensitive to can be identified, a serum can be developed that, when administered to the pet in injections, reduces the pet's sensitivity to the allergens over time.
Sometimes, the cause of an allergic skin problem can't be determined right away. Fortunately, your vet can frequently use medication to treat the itching without finding out exactly what the pet is allergic to. Although this is not a "cure", the pet can be made more comfortable. In general, the best remedy is to avoid whatever it is that sparks the allergic reaction.
Bacterial skin infections
All people (and pets) have bacteria on their skin. In most cases, these bacteria don't cause a problem. However, if the skin is damaged, such as by scratching, or is unhealthy because of another disease (for example, hormonal problems), a bacterial infection can develop.
Bacterial skin infections, called pyoderma, are not contagious to people or other pets. However, they can cause pustules, crusts, open wounds, and infections that damage the hair follicles (leading to hair loss), and can become a serious medical issue for affected pets.
Bacterial skin infections are usually diagnosed based on the patient's medical history and the location and appearance of the affected area. Your vet may also want to take a skin sample to look at the cells or to perform bacterial culture and sensitivity or other laboratory testing to determine the cause of the unhealthy skin and the most appropriate treatment. Many bacterial skin infections have an underlying cause, such as a parasite infestation, hormonal or immune system disorder, or allergy. If the underlying cause is not treated appropriately, the skin infection will likely return. In addition to treatment for the underlying cause, your vet may recommend antibiotics, which can be administered in many forms, including pills, injections, shampoos, gels, ointments, and sprays.
Fungal skin infections
The most common fungal organism that causes skin problems in pets is a yeast called Malassezia. Malassezia infection generally occurs secondary to another skin problem, such as allergic skin disease or a bacterial skin infection. Fortunately, Malassezia infection is treatable through a variety of methods (including shampoos, gels/ointments, and pills). The key to resolving the problem for good is to successfully manage the underlying condition.
Ringworm is not a parasite but is actually a relatively common fungal skin infection which causes scaly, crusty skin lesions and hair loss. It can occur anywhere on the body but commonly affects the head and legs. Sometimes the area of hair loss is circular, but not always. Diagnosis is best made from a fungal culture. For this test, your vet will pluck a few hairs from an affected area and place the sample in a special solution to see if the ringworm organism grows.
Ringworm is treatable, usually with medicated baths, ointments/gels, or pills, but complete eradication of the infection can take a month or longer.
Ringworm can be quite contagious to people and other pets. Therefore, children and other household pets should be kept away from an infected pet during the treatment period. People who come into contact with the affected pet should wash their hands regularly.
Parasitic skin diseases
A number of parasites can infest dogs and cats. They can cause itching, which may lead to self-mutilation from excessive scratching and biting and other trauma to the skin. Fleas are one of the biggest culprits.
Pets that are allergic to fleas may scratch excessively, causing redness, wounds, pustules, scabs, and hair loss in the affected areas. Even some pets that aren't allergic to fleas still experience itching and general misery from these parasites. Other small parasites, such as ticks, chiggers, lice, and biting flies, can also bother pets. For most of these parasites, your vet can recommend a product to control them and protect your pet from their effects.
Mites that can affect dogs and cats include ear mites (which are contagious among pets and cause severe itching and ear infections); sarcoptic mites, which burrow in the skin, causing intense itching and skin lesions (known as scabies or red mange), and are contagious to people in the household; and Demodex mites, which are more common in dogs than in cats and are associated with itching, hair loss, and skin problems. Demodex mites are not contagious.
Most parasitic skin diseases can be diagnosed through direct visualisation of the parasite (such as fleas), or by examining small samples of skin or debris under a microscope to diagnose the problem (such as ear or Demodex mites). All of these parasitic conditions are treatable, so if your pet is itching or you notice any bald areas or skin wounds, contact your vet.
The skin problems listed above are the most common ones that affect dogs and cats, but there are many others, including immune-mediated skin disease, cancer involving the skin, and endocrine (hormonal) problems that affect the skin. Most skin conditions can be controlled, and some can be cured. No matter the cause of your pet's skin problem, it is possible to ease his or her suffering. When you do, it will be a relief for both of you.