Cats with flat faces such as Persians, Himalayans, Munchkins, and Scottish Folds are more susceptible to all kinds of respiratory issues.
Upper Respiratory Infection
An upper respiratory infection may be caused by any number of viruses such as chlamydia or bordetella, but often turns into a secondary bacterial infection so it is usually treated as such.
Fungal Infection
Fungal infections are not seen often in cats due to their immune system, but sometimes, a cat can breathe in the spores from a fungus such as cryptococcosis or aspergillosis. These are both quite rare, but the cause is usually from inhaling spores around pigeon droppings.
Herpes Virus
Cats are able to catch herpes from other cats with the virus and it is common in cats who spend a lot of time outside. The virus is known to go into remission and recur during times of stress. There is no cure and it is not contagious to humans.
Feline Calicivirus
Feline calicivirus is a common and extremely contagious virus that spreads between cats through direct contact. It usually only affects the mouth where it causes ulcers, but it is also known to affect the respiratory tract. It can affect both indoor and outdoor cats but is more common in cats that live in multi-cat households.
Feline Leukemia
This is the second leading cause of death in cats, affects about 3% of all cats, and is fatal in 85% of infected felines within the first three years of transmission. Feline leukemia attacks the immune system and can also cause anemia. This virus is passed from other cats through bodily fluids such as saliva, blood, urine, and feces. Cats in multicat households and outdoor cats have a higher risk of contracting feline leukemia.
Allergies
Although allergies are not uncommon in cats, it usually affects the skin rather than the respiratory system. However, cats that show sensitivities in other ways (dermatitis, vomiting, itching) are more susceptible to respiratory allergic reactions. With the sneezing, your cat will probably also have red eyes, sometimes runny, and agitation.
Nasopharyngeal Polyps
Nasal polyps are not common in cats but have been seen in cats that previously had upper respiratory infections. It is just a mass of tissue in the upper respiratory tract that usually affects kittens and young cats. If your cat is having trouble breathing, shakes her head, and has difficulty in swallowing, they may have nasal polyps.