Believe it or not, humans are not the only creatures hindered by "all powerful" allergies! In fact one of the most common conditions affecting both dogs and cats are allergies! 
In the allergic state, a cat's or dog's immune system "overreacts" to foreign substances to which it is exposed, and these overreactions are manifested in 3 different ways.  The most common is itching of the skin, both generalized or localized (one specific spot).  Another manifestation involves the respiratory system and may result in coughing, sneezing, and/or wheezing.  Sometimes there may be an associated nasal and/or eye discharge.  The third manifestation involves the digestive system, resulting in vomiting or diarrhea.

There are 4 known types of allergies that affect both dogs and cats: contact, flea, food, and inhalant.  Dogs can also suffer from bacterial allergies. 

1.  Inhalant Allergy
The most common type of allergy in both cats and dogs is inhalant, or atopy.  Pets may be allergic to all of the same inhaled allergens that affect humans.  These include tree, grass, and weed pollens, mold, mildew, and dustmites.  Just as with humans, many of these outdoor allergies occur seasonally.  When humans inhale these allergens, we express the allergy as a respitratory problem, often known as "hayfever".  The dog's or cat's reaction, however, usually produces severe, generalized itching.
There are a variety of treatments for cats and dogs suffering from inhalant allergies, and your veterinarian will determine which is most appropriate for your pet.  These include anti-inflammatory medication, shampoo therapy and hyposensitization testing.

2.  Flea allergy
Flea allergy is common in both dogs and cats.  A normal pet experiences only minor irritation in response to flea bites, often without any itching.  On the other hand, the flea allergic cat or dog has a sever, itch-producing reaction when the flea's saliva is deposited in the skin.  Just one bite causes such intense itiching that the pet may severly scratch or chew itself, leading to removal of large amounts of hair.  There will often be open sores or scabs, which can allow a secondary bacterial infection to begin.  The area most commonly affected is over the rump; in addition a cat may have many small scabs around the head or neck.
The most important treatment for flea allergy is to get the pet away from ALL fleas.  Therefore, strict flea control is the backbone of successful treatment.  Medical intervention may also be necessary with the use of corticosteriods to block the reaction and provide relief.

3.  Food allergy
Neither dogs nor cats are likely to be born with food allergies.  More commonly they develop allergies to food products they have eaten for a long time.  The allergy most frequently develops in response to the protein component of the food; for example, beef, pork, chicken, or turkey.  Possible signs of a food allergy include itching, digestive disorders, and respiratory diestress. 
Testing for food allergies is done using a specific veterinary hypoallergenic diet.  Because it takes at least eight weeks for all other food products to get out of the system, the cat or dog must eat the special diet exclusively for 8-12 weeks (or more).  When using a hypoallergenic diet to test for food allergies, the diet MUST be used exclusively...this means no treats or table scraps!

4.  Contact allergy
Contact allergy is the least common type in both cats and dogs.  It results in a local reaction of the skin.  Examples of contact allergy include reactions to flea collars or to types of bedding, such as wool,  If the pet is allergic to such substances, there will be skin irritation and itching at the points of contact.  Removal of the contact irritant solves the problem, although identifying the allergen can require some detective work.

5. Bacterial allergy - DOGS ONLY
There are several species of Staphylococcus (Staph) bacteria that live on normal dog skin.  If the skin is normal and the dog's immune system is functioning properly, Staph causes no problems to its host.  When a dog does develop an allergy to these bacteria, areas of hair loss occur.  These Staph infections are easily treated with antibiotics, but often return as soon as antibiotics are discontinued.  The best way to treat Staph allergy involves using antibiotics to control the immediate problem and desensitization with Staph antigen for long-term relief.

SO...
As you can see, us humans aren't the only ones with runny noses and itchy skin - our pets can be plagued by a multitude of allergies as well! The best thing to do if you suspect your pet is suffering from an allergy is to make an appointment to bring them in for a check-up.  Once the veterinarian can determine just what type of allergy it is, the faster your best friend can get treatment and start to feel relief!!