Allergies to the synthetic polymers are not common, but they can happen. Dogs can develop allergies at any age, and to any substance. Allergies to plastics can be challenging to diagnose due to the prevalence in plastic products. Plastics are often used in the manufacture of pet products like toys, food bowls, and rope, as well as in everyday commodities such as food wrap, shoes, and carpet. Contact allergies can be just as uncomfortable, unsightly, and difficult to diagnose for our canine companions as they are for humans, and medical attention should be obtained to deal with this serious health condition.

Allergies are a hyperactive reaction of the immune system to a protein that the body sees as an intruder. Allergies to fully synthetic polymers such as most plastics are rare but not unheard of.

Skin reactions that are not clustered around the area of contact are generally concentrated under the front legs and between the toes as well as around the face and groin. Dogs often come into contact with plastics in toys, water bowls, and food containers.

Different types of plastic can be found in various products, and your pet may be allergic to just one variety or to many. Some of the most common are:

Polyethylene terephthalate (PET or PETE) - This is used most commonly to make medicine bottles, peanut butter jars, and rope. It is also incorporated into carpet after recycling. 

High-density polyethylene (HDPE) - This is the type of plastic that can be found in milk jugs, small toys, and shampoo and conditioner bottles. 

Polyvinyl chloride (PVC) - PVC plastic should not come into contact with food items and is used most commonly for plumbing pipes and other industrial grade items.

Low-density polyethylene (LDPE) - This is a very flexible plastic, used for sandwich bags, plastic wrap, and plastic grocery bags.

Polypropylene (PP) - Polypropylene can handle higher temperatures and is often employed in the making of Tupperware, stadium cups, and syrup bottles. 

Polycarbonate- Often used in baby bottles, compact discs, and eyeglasses, this plastic has high impact resistance and optical properties.

Contact allergies in canines are brought about by the aggressive response of mast cells to the plastic. Mast cells are specialized cells tasked with the job of protecting the body from pathogens. When the immune system is activated by a particular substance, it manufactures its own protein which causes the mast cells to release histamine. Histamine is a naturally occurring compound that has an inflammatory effect on the tissues it comes into contact with. This results in the itchy and inflamed skin conditions characteristic of an allergic reaction in canines.

The general physical should reveal the symptoms that are characteristic of a contact allergy. This will prompt your veterinarian to collect a skin sample, using a method known as a skin scraping. The skin samples obtained by scraping will then be examined by cutaneous cytology, a microscopic evaluation of the skin cells that is completed in order to find problems like mites or yeast infections. Allergies to plastic cause skin reactions are often positioned around the face and groin, as well as under the front legs and between the toes, although they can manifest anywhere on the body. 

If an environmental or contact allergy is suspected, your veterinarian may recommend a patch test for diagnosis, also referred to as an intradermal skin test. Miniscule amounts of the suspected antigens are injected under the skin causing a localized reaction, however, plastic is not a common allergen for dogs or humans it may not be included in the patch test unless a plastic allergy is already suspected. A thorough history of your canine’s health and a timeline of symptoms may be of more assistance in finding an accurate diagnosis.  Many doctors choose to try to diagnose which allergen is causing the reaction by eliminating suspected allergens from the environment first. The prevalence of plastic in the environment can make this difficult.

While oral and topical antihistamines are generally successful in relieving allergy symptoms in humans, they are useful for only twenty to thirty percent of canines and have a tendency to lose effectiveness over time. Salves and shampoos made with hydrocortisone will usually relieve any skin discomfort. It is important to ensure that your pet does not lick the preparation off themselves, however, as the chemicals can be somewhat toxic when ingested. If neither the topical hydrocortisone or antihistamines are successful in reducing symptoms, then corticosteroids may be warranted, either in injection or oral tablet form. 

Although these medications are usually very effective in reducing the signs of allergy in dogs, the side effects can be damaging. The long-term side-effects can contribute to serious disorders such as liver dysfunction and diabetes, so concurrent monitoring of the blood chemistry levels is needed to ensure proper treatment. The lowest effective dose of corticosteroid should always be employed to avoid the dose-dependent side effects. Animals that are afflicted with unavoidable or severe allergic reactions may be given injected immunotherapy, especially in reactions that are resistant to antihistamines and present for at least four to six months of the year. Advancements in sublingual immunotherapy treatments have been made, and recent trials are promising, but this is not a commonly available option for dogs at this time.

If your dog has developed an allergy to plastics, your veterinarian will give you instructions specific to your situation for treating the symptoms until you are able to eliminate or sufficiently reduce the allergen in the environment. Even after symptoms have disappeared, administration of medications may be required, and instructions regarding oral and topical medication should be followed faithfully. In canines, it is common for skin allergies to develop bacterial infections as well, and antibiotics will be prescribed in those cases. Stopping the administration of these antibiotics before all of the bacterial infection has been eradicated may cause the infection to reoccur.