Contact dermatitis is inflammation of the skin caused by something that touches it. A University of Minnesota veterinary dermatology handbook describes it as an itchy, inflamed skin response to contact with an irritating or allergy-causing substance [1]. It is uncommon in dogs, cats and other domestic animals, but the handbook adds that it may be missed more often than we think, because it is hard to diagnose [1].
In pets, one well-known example is a reaction to medicine put on the skin or in the ears. The same handbook lists ear medicines and ear cleaners among the things that can cause an irritant or allergic reaction in the ear [2].
If your pet’s skin or ear flap gets red, swollen or sore after a new medicine or product, call your vet. Do not stop or change a prescribed medicine on your own.
Two kinds of contact dermatitis
- Irritant: the substance damages the skin directly. No earlier exposure is needed, and a stronger substance or longer contact tends to cause worse damage [1].
- Allergic: the immune system has learned to react to the substance after earlier exposure, sometimes over weeks or months. Once that has happened, even a small amount can set off a reaction [1]. An older review calls the allergic form rare in dogs [3].
Many substances can act in both ways [1]. Moisture on the skin makes a reaction more likely, because it weakens the skin’s natural barrier [1].
Common causes
The handbook lists many possible triggers for dogs and cats [1], including:
- some garden and house plants, and grass;
- medicines put on the skin or in the ears, and the liquids they are mixed in;
- shampoos, sprays and other products used on the coat, including flea and tick products;
- household and building materials such as plastic, cement, wood, paint and carpets;
- soaps, detergents, solvents and garden chemicals.
The handbook also points out that the cause is often something that has been around the pet for a long time, not something new [1].
Where it shows up
Contact dermatitis usually affects skin with little or no hair, where a substance can touch the skin easily: the belly, groin, armpits, chest, the underside of the paws, the scrotum and the area under the tail [1]. An older review of dogs also notes thinly haired skin and the feet [3].
The pattern can give clues. The handbook notes that a reaction spread over the haired body may point to a shampoo, a patch between the shoulder blades to a spot-on parasite product, and sores on the inner side of the ear flap usually to ear medicine [1].
Ear medicine reactions
The best-described form in pets is a reaction to ear medicine. In an ear that is being treated for otitis externa (inflammation of the outer ear canal), ear drops or ear cleaners can themselves irritate the skin or trigger an allergy [2]. The handbook advises vets to consider this when an ear gets worse after treatment has been started properly [2], and to ask owners to get in touch at once if the ears become redder or new sores appear during treatment [2].
For ear infections themselves, see ear infections in dogs and cat ear mites and ear problems.
Signs of contact dermatitis
Early signs include red skin, swelling and small bumps [1]. Over time, the skin can thicken, darken, flake and crack [1]. Itching tends to be mild to moderate, often less than the skin’s look would suggest [1]. Pain and soreness fit better with an irritant reaction, and itching with an allergic one, but the two often look alike [1].
Because itching can lead to scratching and licking, some signs come from the pet’s own damage to the skin, and a bacterial or yeast infection can develop on top [1][3].
How vets find the cause
Contact dermatitis can be hard to pin down. The first signs do not last long, and by the time a pet is seen the skin often shows mostly the effects of ongoing inflammation and scratching [3].
Your vet will rely on a careful history and on where the skin is affected [1]. Useful facts include whether it has happened before, whether other animals in the home are affected, which medicines and products are used, and what surfaces and plants your pet touches [1]. An irritant often affects several animals in a household, while an allergy usually affects only one [1].
The most practical test is to remove every possible trigger from the skin, coat and surroundings, under your vet’s guidance, and see whether the skin settles [1]. A vet may then, in some cases, carefully re-expose a small area to confirm the cause [1]. This is not done after a severe reaction or with a strong irritant [1]. A patch test is the reference test for the allergic form, but it is hard to carry out in animals [1].
Other problems can look similar, such as other allergies, mange and skin infections, so your vet may need to rule them out [1].
Tell your vet about every product used on your pet’s skin and ears, including any new medicine.
How vets treat it
The best treatment is to find the cause and keep your pet away from it, although the cause is not always found [1]. Your vet may advise rinsing the substance off the skin and coat with water or a mild shampoo [1], and may prescribe medicine to calm the inflammation and itching [1]. Any infection on top is treated as well [1].
If the ear infection still needs treatment, your vet will decide how to treat it.
At home, as directed by a vet:
- stop or change a medicine only when your vet tells you to;
- do not put any new product on the skin or ears unless your vet tells you to;
- give all prescribed medicines exactly as directed;
- stop your pet from scratching or licking the area in the way your vet advises;
- tell your vet about every product your pet comes into contact with;
- go back for every recheck.
Outlook
Outcomes vary between pets:
- An older review of allergic contact dermatitis in dogs reported a good outlook when the cause was removed and the inflammation was treated [4].
- The University of Minnesota handbook notes that improvement may be limited when the cause cannot be found and contact goes on [1].
These are general statements. They cannot predict how one pet will do. Your vet can explain what this means for your pet.
When to see your vet
Call your vet if your dog or cat has:
- red, swollen skin on the inner ear flap, or ears that get redder, during ear treatment [1][2];
- bumps or sores on the ear flap or on thinly haired skin [1][3];
- new itching or pain after a new product or medicine [1][2];
- sores or skin changes on the feet, belly or other thinly haired areas [1][3].
See your vet again if the skin does not improve, gets worse, or the reaction comes back.
FAQ
Can ear drops cause a skin reaction?
Yes. Ear medicines and ear cleaners can cause an irritant or allergic reaction [2]. Call your vet; do not stop the medicine on your own.
Can something my pet has touched for years suddenly cause it?
Yes. The allergic form needs earlier exposure, and the cause is often something that has been in the pet’s life for a long time [1].
Is contact dermatitis common?
Not very. It is described as uncommon in domestic animals [1], and the allergic form as rare in dogs [3].
Will it go away?
It varies, and no one can promise it. See the Outlook section above. Finding and avoiding the cause is the main part of treatment [1].
The bottom line
Contact dermatitis is a skin reaction to something that touches it. It mostly affects thinly haired skin such as the belly, paws and inner ear flap, with redness, bumps, itching or soreness. Ear medicines are a well-known cause in pets, along with plants, coat products and household materials. Call your vet, tell them about every product you use, and do not stop or switch medicines on your own.
This article is for general information only and does not replace advice from your veterinarian. If your pet’s skin reacts to a medicine or product, call your vet.
Sources
- Torres SMF. 2.7 Contact Dermatitis: Small and Large Animals. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota, 2025. CC BY 4.0. https://open.lib.umn.edu/animaldermatology/chapter/contact-allergy-small-and-large-animals/
- Torres SMF. 2.10 Otitis Externa: Dogs and Cats. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota, 2025. CC BY 4.0. https://open.lib.umn.edu/animaldermatology/chapter/otitis-externa-dogs-and-cats/
- Olivry T, Prélaud P, Héripret D, Atlee BA. Allergic contact dermatitis in the dog. Principles and diagnosis. Vet Clin North Am Small Anim Pract. 1990;20(6):1443-56. https://pubmed.ncbi.nlm.nih.gov/2251735/
- Thomsen MK, Kristensen F. Contact dermatitis in the dog. A review and a clinical study. Nord Vet Med. 1986;38(3):129-47. https://pubmed.ncbi.nlm.nih.gov/3529032/