Proteins in the urine of cats will also trigger allergic reactions. Some animals seem more tolerable than others because they shed fewer allergens. Unfortunately, there are no non-allergic animals. It is also true that the length of hair does not alter the animal's allergenicity. Within any given breed, or even litter, you may find animals that you can tolerate better than others.
Allergies are usually cumulative.
Since the allergic person is sensitive to more than one thing, it is the Total Allergen Level that causes a reaction. Whether or not a person has symptoms depends on how many allergens are in the environment at the same time. An individual who is allergic to animals may exhibit no noticeable symptoms when the total exposure is below his allergy threshold level. The trouble begins when there are enough allergens in the environment to exceed this level. The goal is to minimize exposure to airborne allergens that exceed tolerance thresholds and trigger attacks.