Like people, dogs suffer from various allergies. In most cases, allergic reactions are annoying but not life-threatening. Sometimes allergies express themselves as urticaria (hives), a condition characterized by small bumps in the skin. Sometimes, but not always, the bumps are itchy. A related condition is angioedema, or swelling of the face, especially around the muzzle and eyes. These reactions typically develop within 20 minutes of exposure to the allergen. They aren't usually life-threatening, although severe swelling around the throat can make breathing difficult for certain breeds, like Bulldog, for example. The usual treatment for allergies is antihistamines, but if breathing is affected, epinephrine is administered.
Some research suggests that about one third of all allergies are caused by foods. If you suspect your animal has a food allergy, try the following diet, which omits the common allergens implicated in both animal and human conditions: beef, wheat, milk, eggs, nuts, fruits, tomatoes, carrots, yeast and various spices and additives. If the problem clears up during the diet, then slowly re-introduce foods one at a time to find out which one or ones are causing the problem. To give the diet an adequate chance, keep your animal on it for at least two months. If your pet's condition has not improved by then, the cause of its problem may not be an allergy, or there is still an offending substance in the food.
One of the most severe allergic reactions is anaphylaxis, a life-threatening condition that may include shock, respiratory and cardiac failure, and death. Anything that can cause an allergic reaction can cause anaphylaxis, including stings, antibiotics, vaccines or other medications, and even foods. It is rare but deadly. Common signs include sudden diarrhea, vomiting, pale gums, fast heart rate, shock, seizure, coma, and death. Unlike many other kinds of allergic reactions, there is no facial swelling. Anaphylaxis is an extreme health risk. Immediately drive to the nearest vet clinic.
While it is not known exactly what may cause animals to react so badly, dogs who have previously had an allergic reaction (like hives) are most at risk. If your dog suffers severe allergic reactions that affect his breathing, you may be able to secure an "epi-pen" from your vet. An epi-pen is a syringe and needle containing a single dose of epinephrine for future emergencies. There is no real cure for allergies, but several treatment options are available, ranging from avoiding the allergen (not easy), administering special shampoos and oils, to dispensing drugs.