Allergy to cats
Cat allergy in humans is an allergic reaction to one or more allergens produced by cats. The most common of these allergens are the glycoprotein Fel d 1, secreted by the cat's sebaceous glands and Fel d 4, which is expressed in saliva. An allergic reaction is a histamine reaction that is usually characterized by coughing, wheezing, chest tightening, itching, nasal congestion, rash, watering eyes, sneezing, chapped lips, and similar symptoms. In some severe cases, reactions may progress rapidly to cause the victim's airway to become inflamed and close up, requiring emergency medical attention. Those with severe, life-threatening cat allergies face tremendous challenges due to lack of public awareness about anaphylactic cat allergies, and do not enjoy the same conscientiousness from the public as those with a food allergy might, due to widespread knowledge of allergies to allergens such as nuts or dairy.
Five cat allergens have been described in medical literature. The two major allergens are Fel d 1 (a secretoglobin) and Fel d 4 (a lipocalin). The minor allergens include Fel d 2 (an albumin), Fel d 3 (a cystatin), and cat IgA.
Fel d 4 is the product of the cat major urinary protein gene. It is primarily expressed in the submandibular salivary gland and is deposited onto dander as the cat grooms itself. A study found that 63% of cat allergic people have antibodies against Fel d 4.
Symptoms of an allergic reaction to cats range from mild to severe, and include swollen, red, itchy, and watery eyes; nasal congestion, itchy nose, sneezing, chronic sore throat or itchy throat, coughing, wheezing, asthma, hay fever, hives or rash on the face or chest, or itchy skin. If a cat has scratched, licked, or bitten someone who is allergic to cats, redness and sometimes even swelling of the affected area will occur. For those severely allergic, a reaction may resemble that of someone with a severe food allergy, and such reactions require emergency medical care. 
Coping with allergies
Allergens are airborne survive for months or even years by themselves, hence removing anything that can trap and hold the allergens (carpet, rugs, pillows) and cleaning regularly and thoroughly with HEPA filters and electrostatic air purifier systems reduces risk. Frequent hand washing, especially after handling the cat, and washing hands prior to touching eyes, nose, or mouth, and limiting the cat's access to certain rooms, such as the bedroom or other rooms where much time is spent, may also reduce allergic reactions.
Cat allergies can often be controlled with over the counter or prescription medications. Antihistamines and decongestants may provide allergy relief.
Synthetic epitope vaccine
The Synthetic epitope vaccine is an in-development vaccine to provide a long term vaccine for allergies.
Regularly bathing the cat may remove significant amounts of allergens from the fur. Furthermore, regularly brushing the cat will reduce the amount of loose fur (and its attached saliva) in the air. Feeding the cat a high quality diet with plenty of omega-3 fatty acids will help keep the coat healthy and minimize dander.
A hypoallergenic cat is a cat that is less likely to provoke, or produce an allergic reaction in humans. Although the topic is controversial, owners' experience and recent clinical studies suggest that Siberian cats, Devon Rex and Cornish Rex cats, Abyssinian cats, Balinese cats, and several other breeds, especially females, are likely to have low levels of Fel d 1, the main allergenic protein.
From among the above cats noted, the most popular cat breeds to be renowned for their hypoallergenic quality is the Siberian and Balinese cat breed. These cats have been noted to produce much lesser amounts of the protein allergens in comparison to regular domestic household cats, and other cat breeds. Cats that have some Balinese cat lineage or ancestry might have a probability of producing few amounts of the protein allergens, some cat breeds that might have some Balinese cat lineage include the Oriental Shorthair, Oriental Longhair, and some Siamese cats.
The common theory among these two hypoallergenic, medium to long-haired cat breeds is that their long-haired gene is associated with producing lesser amounts of the allergens. This may be the case as the Balinese cat, a medium to long-haired cat breed; also referred to as the Long-haired Siamese cat is regarded as hypoallergenic, where as the Siamese cat, a short-haired cat breed is not. Some Siamese cats might possess hypoallergenic qualities if they have proven Balinese cat ancestry, they are often referred to as short-haired Balinese cats. This might provide some evidence that the long-haired genes or traits within this cat breed have resulted in a cat that can genetically produce less amounts of the cat allergens.
In 2006, the Allerca company announced the successful breeding of a line of hypoallergenic cats. However, no peer-reviewed studies have been done to confirm their claims and many scientists and consumers are skeptical of the company's assertions. The company has announced that on January 1, 2010 they will cease their breeding activities.
Another company, Felix Pets, also claims to be developing a breed of hypoallergenic cat.
Cat sex and color
Female cats produce a lower level of allergens than males, and neutered males produce a lower level of allergens than unneutered males. In 2000, researchers at the Long Island College Hospital found that cat owners with dark-colored cats were more likely to report allergy symptoms than those with light-colored cats. A later study by the Wellington Asthma Research Group found that fur color had no effect on how much allergen a cat produced.
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