​Pets produce dander  (microscopic skin flakes that they shed), and the protein in it can cause severe allergic reactions for some people.

Pet dander is a little like dandruff flakes, only smaller; at around 2-3 microns in size it easily becomes airborne and can be inhaled. ​

​Dander can cause allergic reactions for a long period and may persist for many months after the pet has left the house.  

​​The origin of the allergens is in the pet’s urine, sweat and saliva. These excretions adhere to their skin, for example when they clean themselves, and become of the dander they shed.

​Cat dander is the most commonly inhaled allergen after house dust mite and pollen. Other types of pet, such as dogs, mice and guinea pigs, may similarly cause allergic reactions.

​Because they are so light, pet allergens are widely distributed in the air, remaining airborne for several hours before settling, only to be easily stirred up into the air again.

Clearly, the best way of avoiding pet dander is to not have a pet! However, many of us love our pets too much to do without them! In that case, there are various measures you can take to reduce your exposure, including controlling the pet’s access to certain rooms, and using an effective air purifier to neutralise the dander.

​Pet allergies are known to play a role in:

• Asthma - around 40% of people with asthma are sensitive to cat allergen.
• Atopic dermatitis - characterised by a skin rash.
• Conjunctivitis - an inflammation of the linings of the eyelids.
• Rhinitis - a runny nose and sneezing.

​People with a tendency to allergy (known as atopy), should avoid owning pets if possible. Unfortunately, some people who don’t initially exhibit allergic reactions, can nevertheless develop symptoms after continued exposure.

​Allergens usually enter the respiratory system through the nose. Mast cells in the airways release mediators, which trigger the allergy attack. This attack is an overreaction of the body’s immune system to the invading allergens that have bonded with antibodies. Mast cells are one of the human body’s principal defences against allergens and are found in connective tissue and mucous membranes. One of its biological functions is innate immunity including involvement in host defence mechanisms against parasitic infestations, tissue repair, etc.

​​Pet dander is very ‘sticky’ and can stay in your hair, clothes and other belongings for long periods of time. This is why you can still suffer symptoms when you are away from the pet causing those symptoms.

The major cat related allergens are found in the cat’s sweat and saliva and the major dog related allergen is found in its saliva.

Perhaps the best pets for a pet allergy sufferer are fish, as they are not associated with allergy!

​Before turning to technological or other solutions, careful allergen avoidance / environmental allergen control is important. For example:

• Do not let your pet roam the entire house, as it will shed allergen-containing dander wherever it goes, and that dander persists for months, both in the air and on the surfaces it sticks to.
• Never allow your pet to enter the bedroom of an allergic person. The worst thing you can do is to allow the animal onto the bed itself.
• If practicable, confine your pet to an outdoors dry and comfortable shelter, or to just one well-ventilated room. This gives the person who suffers with the allergy the best chance of controlling their symptoms. If your pet is to be allowed controlled access to the house, the kitchen, with its lack of soft furnishings, is a good choice.
• If possible, and if you spot it in time, put a cat outdoors as soon as it starts washing itself because this is when allergen starts to spread.
• Reduce dander spreading by washing your pet regularly with an allergen shedding control shampoo, such as PET+, which claims to reduce allergen load by more than 85%.
• Cuddling your pet is part of the fun of ownership, and it is therapeutic for both of you, but be sure to thoroughly wash your hands afterwards, otherwise you will in turn quickly spread any dander on your hands to surfaces and the surrounding air. Similarly, don’t touch your face if your hands have dander on them as it will quickly reach your eyes and lungs.
• If your dog has hair that moults, ask someone to brush its coat regularly outside to remove excess hair and prevent it moulting in the house.
• Your carpets, curtains and soft furnishings become a reservoir of pet dander wherever your pet has been. So be sure to vacuum regularly with a vacuum that collects dander efficiently and doesn’t leak it back into the atmosphere, and damp dust daily (rather than using a dry duster).
• If practical, consider reducing soft furnishings and carpets.

While numerous manufacturers of ‘air cleaners’ / ‘air filters’ claim to be able to clear pet dander from the air, they can only reduce, not eliminate, the problem, because:

• they can only clean the air that passes through them, and some air in the room never passes through the filter
• they don’t clean surfaces at all and it only takes a small disturbance to put settled dander back into the air

​There is a long history of disease caused by inhaled particles that stretches from observations by Agricola and Paracelsus in the 15th and 16th centuries up to the present. In the 20th Century the twin scourges of asbestos and crystalline silica (quartz) exerted a terrible toll of death and disease. The bad old days when these dust related lung diseases were common are fortunately gone but as we move into the 21st century a new particle type, the ultra-fine particle, has emerged as one with a potential role in causing disease. 

​Ultrafine particles (UFPs) are particulate matter of nanoscale size (less than 0.1 μm or 100 nm in diameter). This size class of ambient air pollution particles, which are far smaller than the regulated PM10 and PM2.5 particle classes, are believed to have several more aggressive health implications than those arising from larger particulates.

​There are two main divisions that categorise types of UFPs. UFPs can either be carbon-based or metallic, and metallics can be further subdivided by their magnetic properties.

​UFPs are the main constituent (by number) of airborne particulate matter. UFPs arise from a range of indoor sources that including printers and copiers, cooking, tobacco smoke, vaping, candles, chimney cracks and vacuum cleaners. Those indoor sources are often considerably supplemented by the penetration of contaminated air from outside, where vehicles and industry are the major contributors.

​Unlike their larger PM10 and PM2.5 brethren, UFPs that are inhaled, because they are very small, can penetrate tissue and / or be absorbed directly into the bloodstream where effects may become apparent quickly.

​Exposure to UFPs, even if the underlying materials are not very toxic, may cause oxidative stress, inflammatory mediator release, and could induce heart disease, lung disease, and other systemic effects. A robust association has been observed between fine particulate levels and both lung cancer and cardiopulmonary disease.

​The exact mechanism through which UFP exposure leads to health effects remains to be fully understood, but effects on blood pressure may play a role. It has recently been reported that UFP is associated with an increase in blood pressure in schoolchildren with the smallest particles inducing the largest effect.

​Standard HEPA filters as fitted to almost all air cleaners only collect particles down to around PM2.5 although specialist HEPA filters such as 'HyperHEPA clean room grade filters' can collect particles across much of the ultra-fine spectrum.

​Ion generators have been found to have mediocre UFP removal performance and ultraviolet germicidal irradiation (UVGI) has demonstrated very limited or no UFP removal capabilities.

​In this approach, the ultra-fines are subject to in-situ oxidation by hydroxyl radicals. Oxidation by hydroxyls is known to fragment organic carbon ultra-fine particles, which typically constitute most ultra-fines indoors, changing them over time from solids to harmless gasses.