UNDERSTANDING YOUR DOG

PART 1: THE SKIN

The skin is the largest organ in the body but often the most overlooked. It comprises two major layers: the epidermis and the dermis. The dermis and epidermis work together to maintain the integrity and function of the skin. The epidermis acts as a protective barrier, while the dermis provides structural support and facilitates various physiological processes. Skin conditions, including rashes and infections, can affect both layers and may require veterinary attention for proper diagnosis and treatment.

THE EPIDERMIS

The epidermis is mostly made up of cells called keratinocytes. These cells start their lives on the innermost part of the epidermis, and as they mature, they grow outwards towards the outermost layer, flattening and drying as they go to form a hard surface layer. This whole process takes between three and six weeks, depending on the part of the body and the thickness of the skin in that particular area. The primary role of keratinocytes is to prevent harmful substances from getting into the body, so these cells are held together with tight connections. These connections stop bacteria and water from getting in and prevent too much water from getting out.

Other cells in the skin include the following:

• Melanocytes: These are the cells responsible for producing pigment. They are the reason some dogs have darker skin than others and why some dogs have dark patches.

• Langerhans cells: These spider-shaped cells of the immune system act to gather information on intruders and signal the attack.

THE DERMIS

The dermis is the second layer of skin beneath the epidermis. It plays a crucial role in providing support, nourishment, and resilience to the skin. Some key components of the dermis include:

• Connective tissue: The dermis primarily comprises connective tissues, including collagen and elastic fibres. Collagen provides strength and structure, while elastic fibres contribute to the skin's elasticity.

• Blood vessels: The dermis is richly supplied with blood vessels that deliver oxygen and nutrients to the skin cells. These vessels also play a role in regulating body temperature.

• Nerve endings: The dermis contains sensory nerve endings that transmit information about touch, pressure, pain, and temperature. These nerve endings are essential for the dog's ability to sense and respond to its environment.

• Hair follicles: Hair follicles, which extend from the epidermis into the dermis, are responsible for hair growth. The dermal papilla at the base of the follicle is connected to blood vessels, supplying nutrients necessary for hair growth.

• Sebaceous glands: Sebaceous glands are present in the dermis and produce sebum, an oily substance that helps moisturise and protect the skin and hair.

• Sweat glands: Dogs have fewer sweat glands than humans, and most of them are located in the paw pads. Sweating is not a primary means of temperature regulation in dogs; instead, they primarily regulate body temperature through panting.

• Immune cells: The dermis houses immune cells that play a role in defending the body against infections and foreign substances.

SYMPTOMS OF SKIN CONDITIONS

Skin has only a limited number of ways that it can show symptoms. After all, there aren't many cells present, and they all react in a certain way.

Symptoms of skin problems include:

• Redness

• Pimples

• Rashes

• Thickened skin

• Itchiness

• Hair loss

REDNESS

When skin goes red, it is usually because the blood vessels in the area open wide (called dilating) and let more blood into the area. They do this in response to messenger signals from cells, such as the chemical IL-1. Messenger signals get released in response to messages coming from the outside (such as from the Langerhans cells recognising bacteria) or messages going outwards (such as pain signals from the brain). IL-1 is picked up by cells and starts a chain reaction, resulting in the dilating of the blood vessels and the rushing of blood to the area to prepare for the threat.

RASHES

Most rashes are red for the reasons outlined above, i.e. the body recognises an issue and sends more blood to the area. Many things, including allergies, irritation, parasites, infections and food sensitivities can cause rashes.

THICKENED SKIN

Skin becomes thicker for one of two main reasons. Either the body is producing too many new skin cells (the body recognises a higher turnover of cells secondary to inflammation, so it produces new cells at a faster rate), or because the dead skin cells are not falling away from the body correctly (because they are not being 'programmed' properly, and don't die at the right time).

ITCHINESS

Itchiness (properly called 'pruritis') is a very common symptom of skin diseases. In the case of allergic reactions, three major steps are involved in 'feeling' an itch. First, immune cells that are on the lookout for bacteria and foreign bodies recognise the allergen and release a messenger signal. This messenger signal starts a chain reaction, which triggers nerves to transfer messages to the brain. The brain then tells the dog to scratch the itch. The problem with this is that scratching damages the skin, making it more prone to feeling itchy. This is referred to as the 'itch-scratch' cycle.

HAIR LOSS

Hair loss, or alopecia, can occur for a number of different reasons:

1. Because an animal is itchy, they may break their hairs early and lose more than they usually would due to the scratching.

2. The hair growth-loss cycle can become disrupted because the hair follicle becomes inflamed, infected or affected by parasites.

3. Hormonal changes and stress can also halt the cycle, causing hair loss.

DISEASES OF THE SKIN

The most common diseases affecting the skin include the following:

ALLERGIES

Whilst 1 in 10 allergic dogs react to their food, most allergic dogs are actually allergic to something in their environment. This is referred to as 'atopy' or 'atopic dermatitis'. For these dogs, allergens trigger the immune cells in the skin, causing an itch response. The skin often appears red and inflamed.

IRRITATIONS

Dogs can develop contact dermatitis from coming into contact with irritating substances such as certain plants and chemicals.

LICE AND FLEAS

Lice and fleas are major tormenters of our pets. Lice and flees hide amongst the hairs and cause serious itching, which may allow infection to enter the skin.

MANGE

Mange is caused by mites, and there are different types including Sarcoptic mange (scabies) and demodectic mange. Symptoms may include hair loss, redness, scabs and intense itching.

HOT SPOTS

Hot spots (otherwise termed ‘acute moist dermatitis’) are localised areas of inflamed, infected skin that are commonly intensely itchy. They can develop quickly and are commonly seen in dogs that repetitively lick, chew or scratch a specific area.

YEAST DERMATITIS

Yeast dermatitis can occur in areas where there is a warm and moist environment, such as in skin folds. It often causes red, itchy and odorous skin.

BACTERIAL INFECTIONS

Bacterial infections commonly result from breaks in the skin, often caused by injury, scratching or chewing. Symptoms may include redness, pustules and crusting.

RINGWORM

Despite its misleading name, ringworm is actually a fungal infection, not a worm issue. It tends to cause circular, raised lesions with a loss of hair in the affected areas.

PYODERMA

Pyoderma is an infection of the skin. It can occur in several layers, right out in the superficial skin layers or deeper down. Pyoderma is highly itchy, and there is usually evidence of pimples or a rash. Pyoderma is unusual except for in immune-compromised individuals or individuals with injuries or damage to the skin. This is because the skin usually fends off infection pretty well thanks to the tight junctions and the immune cells living in the upper layers, so infection is more common in young pets, older pets with a disease, or pets with diseases of the skin that mean it's not functioning properly.

HORMONAL ISSUES

Conditions like hypothyroidism or Cushing’s disease can affect a dog’s skin or coat, leading to issues like hair loss and changes in skin pigmentation.

FINAL THOUGHTS

If you notice any changes in your dog’s skin, such as redness, itching, hair loss or sores, you must consult with your vet. Proper diagnosis is essential for effective treatment, which may include medications, dietary changes, topical treatments or other interventions, depending on the specific condition.