You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Skin allergies are very common in dogs and cats. One of the environmental factors that most often tests positive is "house dust". What does this mean ?

Itchiness (called pruritus) is the main sign associated with skin allergy. In addition, affected animals may have reddened skin, and later skin thickening and black pigmentation. Hair loss (alopecia) often occurs in affected areas of the body, and secondary bacterial infection is a common complication.

To determine the underlying cause of allergic skin disease veterinarians perform intradermal skin tests in which a series of likely allergic factors (called allergens) are injected into the skin , and the local reaction (if any) that results is measured. A large local reaction (swelling - called a wheal- and redness in the skin) suggests that the animal is sensitized to that substance. It is very common for "House Dust" to provide a positive result, and allergic animals often show a positive reaction to more than one factor.

House dust is composed of a variety of many different types of materials including :

• Shed skin cells from humans and animals
• Shed hair fragments from humans and animals
• Moulds
• Fibres from plants
• Particles from food
• House dust mites (these are actually arachnids (members of the spider family) and there are 36 species called - Dermatophagoides). These live on debris in the environment.

All of these materials take the form of fine particulate matter that is carried in the air. These fine particles can sometimes be seen "floating" in air when a bright light is shone through them. They can then be inhaled into the nose, upper airway and lungs of people and animals. If the individual is allergic skin irritation and inflammation results.

The concentration of house dust is greatest in some areas of a household - especially carpets and mattresses. House dust mite numbers are particularly high in bedding, and they are also higher in humid (damp), warm environments. Pets live close to the ground and disturb house dust as they walk so they are likely to be exposed to relatively high concentrations during their lifetime.

Because house dust is so common, and most animals will have been exposed to it, interpreting the significance of a positive skin test is difficult. A patient may develop a large reaction to the skin test - because the animal is sensitive having been in contact with house dust before - but house dust may not be triggering the reaction that is causing the disease !

Treatment may involves :

• Reducing exposure to the allergen by vacuum cleaning the environment
• Prevent access to areas of the house with highest house dust content - eg keep the animal on solid floored areas if possible
• Treat the itchiness with anti-inflammatory drugs eg corticosteroids, antihistamines.
• Desensitisation - using vaccines

Updated October 2013