Many trees, grasses, and weeds produce extremely small, light , dry, protein particles referred to as pollen. Pollen is spread by the wind and it lodges in the mucus membranes of the nose and respiratory tract where is stimulates an allergic reaction in a sensitive person. Your genetic makeup predisposes you to develop this allergic reaction, although it may occur at any age. House dust is not a single substance, but rather a mixture of potentially allergic particles. It may contain fibers from various fabrics, cotton lint, feathers, and other stuffing material.
Dust often contains microscopic mites, which live in bedding, furniture, and carpets.
The dust particles that are often visible floating in a stream of sunlight, are dead dust mites and their waste products. It is the waste products of these mites that stimulates the allergic reaction. Household pets are the main cause of allergic reactions to animals. Cats are the number one culprit. It is now known that pet allergy is caused by the proteins present in animal saliva and not by their fur.