A person can definitely be allergic to one cat and not another. This variability occurs because the immune system of an allergic person reacts to a specific protein, not to the cat’s hair itself. The quantity of this allergenic protein shed into the environment can vary widely from one animal to the next. This difference in protein load determines the severity of a person’s allergic reaction when exposed to a specific feline.
The Primary Allergen: Fel d 1
The cause of nearly all cat allergies is a protein known as Felis domesticus allergen 1, or Fel d 1. This substance is produced primarily in the cat’s salivary, sebaceous (skin), and perianal glands, not simply on the cat’s fur. The protein is a small, highly stable molecule that serves an unknown biological function for the cat itself.
When a cat grooms, Fel d 1 from its saliva transfers onto its coat and skin. Once dry, it flakes off with shed hair and microscopic pieces of dried skin, known as dander. This dander, carrying the Fel d 1, is light and small, allowing it to become airborne easily and remain suspended for long periods. The protein is also durable and sticky, adhering to clothing, furniture, and walls.
For a sensitive person, the immune system mistakenly identifies Fel d 1 as a threat, triggering an allergic response. This involves the production of specific Immunoglobulin E (IgE) antibodies, which bind to the allergen upon re-exposure. The subsequent release of inflammatory chemicals, such as histamine, leads to common allergy symptoms like sneezing, itching, and watery eyes. Fel d 1 is the most significant allergen, responsible for up to 95% of all allergic reactions to cats.
Factors Causing Variability in Allergen Production
The amount of Fel d 1 produced is not constant and depends on several factors specific to the individual cat. This natural variation explains why one cat may provoke a severe reaction while another causes only mild or no symptoms. Hormonal differences play a large part, with unneutered male cats typically producing the highest concentrations of the protein. The testosterone present in intact males appears to boost the production of Fel d 1 in their glands.
Neutering a male cat significantly reduces Fel d 1 production, bringing levels comparable to those found in female cats. The reproductive status of female cats, whether spayed or intact, does not show the same strong correlation with production levels. Kittens also generally produce less of the protein than adult cats.
Genetic factors also contribute to the variability, with certain breeds cited as lower-allergen producers, although no cat is truly hypoallergenic. Breeds like the Siberian and Balinese are thought to produce less Fel d 1 due to natural genetic mutations. Minor factors, such as coat color, have been explored, but Fel d 1 production varies widely between cats, even within the same breed.
Strategies for Diagnosis and Symptom Management
Diagnosis for a suspected cat allergy is typically confirmed through specific allergy testing. A physician may use a skin prick test or a blood test to measure the level of IgE antibodies that react specifically to cat dander or the Fel d 1 protein. Component-resolved diagnosis, which tests for IgE against the recombinant Fel d 1 molecule, provides a highly accurate measure of sensitivity to the major allergen.
Symptom management involves both environmental control and medical intervention to reduce the body’s reaction to the protein. Environmental strategies focus on reducing the allergen load in the home. This includes using high-efficiency particulate air (HEPA) filters, restricting the cat’s access to the bedroom, and regular cleaning with a HEPA-filtered vacuum.
Medical options include over-the-counter or prescription antihistamines and nasal corticosteroids to alleviate immediate symptoms. For a long-term solution, allergen-specific immunotherapy, known as allergy shots, can desensitize the immune system to Fel d 1 over a course of three to five years. Newer, non-invasive methods also exist, such as feeding the cat a specialized diet containing an egg product with anti-Fel d 1 antibodies. This approach neutralizes the protein in the cat’s saliva and reduces the active allergen shed into the environment.