Although they are less likely to cause an allergic reaction than cats, dogs can be the cause of asthma, rhinitis and eczema.
As well as salivary protein in the dander, dogs also excrete allergens in their faces and urine.
Animals with fur and hair are not the only pets that cause allergic reactions.
Birds can also cause allergies, and owners of parrots, canaries, budgies and other birds may become allergic to their droppings and feathers.
This causes a condition known as alveoli is or bird fancier's lung, in which an allergic reaction causes the alveoli or air sacs in the lungs to become inflamed.
In hot countries, in particular, there are numerous reports of cockroach allergy.
In the United States, up to 30 percent of people with allergies, particularly children living in inner city areas are sensitive to the faces and skin particles of cockroaches.
Parrots and cats are among the many pets that can cause an allergic reaction.
For asthma sufferers especially, the only realistic is to avoid having a pet in your home.
Here, plants may grow vigorously but the pollen tends to stay around the farms because there is little wind to blow it into the towns and cities, and little or almost no rain to bring it down to earth.
In most of Africa hay fever is virtually unknown, though in India it is common.
The pollen from cat's tail, also known as timothy grass, is very light and disperses easily in the wind.
It is a common trigger of hay fever.
Workers in orchards and people living nearby can suffer from hay fever in spring, when the trees are in blossom.