Allergies can vary in severity and cause various symptoms. According to the Mayo Clinic, allergies occur when the immune system reacts to a foreign substance by producing antibodies. These antibodies identify a particular allergen as harmful, even when it isn’t. Allergies can cause reactions in the skin, breathing passages and digestive system.

Thousands of people experience allergies to foods, pets and environmental factors. Pets also can be susceptible to allergies. Allergies can be found in cats and dogs, according to PetMD. They also may be present in other animals. People who notice their companion animals scratching, chewing or licking themselves more than normal may find their pets have allergies. Some pets may experience gastrointestinal issues as well.

The pet care information site Pet Cube says common allergens for pets can include:

• pollen from trees, grass and weeds

• food ingredients

• dust mites

• prescription medications

• fleas

• flea/tick control products

• cleaning products

While their human friends may get runny noses or coughs from allergies, symptoms of allergies in cats and dogs tend to take the form of skin irritation, otherwise known as allergic dermatitis. Pet parents should look for the presence of red and irritated skin, hair loss, hot spots, and rashes or hives, in addition to extensive itching or obsessive licking.

Flea allergies are one of the most common sources of allergies for pets. The bite of just one or two fleas per week is enough to cause a reaction. A pet gnawing just at the base of the tail may be suffering from fleas, although other areas may be affected, advises PetMD.

Seasonal and environmental allergies or allergies to foods can result in face rubbing and licking, especially the paws. Skin or ear infections also may occur.

Pets also may be allergic to one another. According to veterinarian Dr. Robert Trimble, co-founder of the San Francisco-based Fuzzy Pet Health, says he’s heard of dogs being allergic to cats and vice versa.

The American Kennel Club urges pet parents to seek help if their pets seem to be itchy all the time. Allowing a pet to scratch or lick for extended periods of time may lead to skin infections with bacteria or yeast. While all allergies cannot be tested, elimination diets and other techniques may help pinpoint sources of allergies. It is essential to speak with a vet to determine how to relieve allergies to help pets feel more comfortable.