My cat has sores on its butt. Is it a grain allergy or something else?

This is probably due to a severe allergy, although it could also be fleas or mites.

 First of all, in order to rule out skin parasites, high quality flea treatment is given. It sounded like your veterinarian has done it already. The next step is to treat the allergy symptomatically and try discovering the cause of the allergy.

 Food can be indeed one the most common cause of it. Some medications can be given by the vet in order to stop the chewing and repair the skin lesions (steroids and antibiotics usually). 

There is also a nice topical spray available, it's called Cortavance and you can get it at the vets.

 Hopefully you will see some results after all this, if not you and your vet should consider starting on a long term allergy treatment.

There could be a couple of reasons why your cat is licking and biting himself. This behavior is a sign of itchiness, and it can be caused by fleas and allergies. Even though he's an indoor cat, he still get them. You could have brought them into the home yourself on your clothes, or a visitor could have brought them in. This does happen; in fact, it happened to my brother and his cats. They were indoors only, and their cats suddenly have terrible fleas that were brought in by a visitor to their home. If your cat isn't up to date on his flea treatment program, I can give you one for him. First, I would give him Capstar. It's a one time pill that starts killing fleas within 30 minutes. Then follow up with a spot on treatment, such as Advantage or Revolution. This is a treatment that has to be used once a month. You will also have to disinfect the environment. Wash his bedding in hot soapy water, and vacuum the furniture and carpet surfaces. You can use a spray to kill fleas in the house, such as Indorex, or a flea bomb would work well to kill the fleas in the home. As for the grain free diet, less than 10% of cats suffering from food allergies, it's the least common type of allergies in pets. If a cat does have a food allergies, it's most commonly related to a protein source, not grains so there is no need for your cat to have a grain free diet unless it's been specifically proven by a vet that he has it. You can switch your cat back to it's regular food. If you are sure he doesn't have fleas, then I would have him seen by a vet. The vet can diagnose if he does have allergies and can prescribe medication to treat his symptoms.

Your cat could have allergies, to fleas, substances in the environment, and most often, to foods. I recommend getting your cat seen by your vet for an exam and treatment and consider doing a food trial. There are commercial foods that have a single protein source. Try feeding your cat a food that contains a protein that he has never been exposed to, such as duck or venison. If his skin improves then he likely has an allergy to the protein in his old food.

I am so sorry to hear about Pee Wee. An allergy to a food is possible though an allergy to grain is much less likely than an allergy to a protein source. With weight loss, however, we worry in older cats about other illnesses such as kidney disease, diabetes, hyperthyroidism, and unfortunately cancer. If your vet has not already done so in the past few months, pee wee should have a bloodwork panel done and potentially X-rays to check for these diseases. Your vet my recommend a prescription diet if they are still concerned about a food allergy.

Certainly both cats could develop an allergy at the same time but more common would be fleas. I recommend to make sure both cats are treated for fleas with a good product like Revolution or Comfortis. To answer your question, the most common allergy is environmental allergies and there are several allergens including dust mites (indoors) and pollen. Food allergies are possible but less common. The most common allergens are fish, chicken and dairy. I hope this helps and feel free to post any additional questions.

Itchy skin like this is often due to one of the following things: 1) Allergies - this can happen suddenly and is usually due to an environmental (i.e pollen) cause. Allergies need to be diagnosed by a veterinarian, because other problems can look similar and the treatment would be different. 2) External parasites - fleas, lice and mites can all cause intense itching. It's best to have a vet check him for mites, because these are microscopic and can cause intense itching. 3) Over-bathing, or using the wrong product for bathing - Bathing too often can cause the skin to get dry and irritated. Cats should normally be bathed no more than once a month with a shampoo that is labeled for cats. If you bathe more than that, or use a shampoo or soap that is meant for people, then you could be damaging the normal protective barrier of the skin. One thing you can do for itchy skin, is give a bath with cool water using an oatmeal or aloe shampoo. You can get these shampoos at the pet store. Do not apply shampoo to the sores - it's better to just flush them with cool water. Considering he is scratching to the point of having open sores, I recommend taking him to the vet for an examination. We can usually discover the cause quickly and provide the most effective treatment. For more information about allergies and itching, I recommend you read the information at the links below. https://www.petcoach.co/article/how-to-tell-if-your-pet-has-allergies/ https://www.petcoach.co/article/4-great-strategies-for-relieving-your-dog-s-allergies/ https://www.petcoach.co/article/skin-allergies-vs-food-allergies/ I hope that helps and Tito gets better soon.

Thanks for using Petco Pet Education Center, formerly Petcoach! This may be due to allergies. It really comes down to figuring out what is causing her allergies so that they can be treated or the specific allergen avoided. There are many things that can cause allergies though in most cases they can be broken down into 3 big categories: flea, food and environmental allergies. Allergies are usually worked up in a stepwise fashion starting with flea allergies as this is the easiest and cheapest to take care of. If not on a flea preventative, then it would be a good idea to get started on one. If already on one then it would be a good idea to change to something else (there are many new products out in the market). If not improved in 1-3 months then it is time to move on and check for food allergies by switching to a novel diet (new protein and new carbohydrate). If that does not seem to be the issue then you are left out having to check for environmental allergies which require blood and/or skin tests. Allergies can be very frustrating to deal with at first but so rewarding at the end when we are able to treat them effectively!