Between 5 and 10% of the human population has an allergy to cat. The major cat allergen is a protein called “Fel-D-1,” which is a protein in the cat’s saliva, sebaceous glands and genitourinary tract. Dried skin particles (dander) contain the protein, even though the protein is not part of the coat itself.
Female cats produce less Fel-D-1 than male cats. Light-colored cats make less than dark-colored cats. Long-haired cats give off less allergen into the environment than short-haired kitties because their long fur holds the protein against the skin.
The Fel-D-1 protein is a very tiny molecule which allows it to stay airborne for a very long time, which in turn makes it easy to inhale. The particles are also very sticky, making it easy for them to cling to furniture, carpet, drapes, bedding and walls — so sticky they can “hang around” six-to-eight months after a cat has left the premises. These particles can also be picked up by shoes and clothing and travel home to abodes that have never housed a cat.
Even “hairless” breeds groom themselves, so the protein ends up on their skin. The only allergic advantage of “hairless” cats is they don’t harbor other allergens such as pollen or dust mites. And even after washing cats, the levels of Fel-D-1 are back up to pre-bath levels within 24 hours.