Lysine Allergy in Cats

Written By hannah hollinger
Published: 04/12/2017Updated: 08/20/2021
Lysine Allergy in Cats - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Lysine Allergy?

Lysine is an amino acid that is used as a supplement in people as well as cats. Lysine will help in improving supplemental calcium absorbency and is often recommended in the treatment of herpes. It works by decreasing the amount of arginine, which is an amino acid that is considered necessary for the herpes virus to reproduce.

Cats with feline herpes will display a respiratory infection with flu-like symptoms like wheezing, fever, lethargy and conjunctivitis (swollen eyes with discharge). Many cats experience exposure to the feline herpes virus however never show symptoms of the illness. If your cat has been exposed to the virus and his immune system becomes weak, the virus may flare up and cause symptoms in your cat. Lysine may also be used for cats that are experiencing allergies.

Lysine is available as a pill or in a powder that can be mixed into your cat’s food. Unfortunately, while lysine has few side effects, some cats will experience an allergy to it.

An amino acid given as a supplement, lysine can be helpful in keeping the herpes virus under control. While it has minimal side effects, should your cat’s immune system overreact, he will experience an allergy.

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Symptoms of Lysine Allergy in Cats

  • Itchiness in your cat’s skin
  • Excessive licking
  • Biting his skin 
  • Skin infection is possible
  • Fur loss may be seen
  • His skin may appear inflamed


 Cats can experience different types of allergies:

Contact Allergies

These occur when your cat’s skin comes in contact with a particular allergen. The allergen will cause a reaction in his skin. Items in your home like disinfectants or chemicals can lead to contact allergies in your cat. 

Flea Allergy Dermatitis

This happens when the saliva from a flea touches your cat’s skin and leads to an allergy. This will lead to itchy skin; your cat’s biting and chewing the areas that are impacted can cause lesions in his skin and his hair can come out in patches.

Inhalant Allergy

This can develop when your cat breathes in particular allergens that are in the air; for example: mold, dander, spores and cigarette smoke. In the case of an inhalant allergy, you may see watery eyes, nasal discharge, coughing and breathing trouble.

Food Allergy

Cats can develop allergies to foods they have consumed for a long period of time. Common allergens include chicken and dairy products.

Causes of Lysine Allergy in Cats

An allergy in your cat will occur when his immune system over-reacts to a protein in something that he is consuming. The response of his immune system is what will cause him to experience itching, inflammation and other symptoms.

Diagnosis of Lysine Allergy in Cats

Should you notice concerning symptoms in your cat, you will want to visit your veterinarian, who will conduct a physical examination. Your veterinarian will ask you questions in regards to the symptoms you have noticed, when you first noticed them and any changes that have occurred. You will also be asked for details in regards to his diet, medications and supplements that he takes and whether there have been any recent changes.

Depending on the physical examination, your veterinarian may conduct a complete blood count, serum chemistry analysis, urinalysis and stool sample evaluation. These will help your veterinarian determine if there is an underlying illness that is leading to your cat’s symptoms. Your veterinarian may obtain a sample of your cat’s skin cells and view them under a microscope to see if mites, fungus or bacteria may be causing your cat’s symptoms. 

If your veterinarian feels that your cat is experiencing an allergy to something he is consuming, like lysine, he will work with you on developing a plan to eliminate different elements of his diet. Should your cat be taking different supplements, your veterinarian may recommend eliminating them first to see if his symptoms are resolved. You can then add them back in one at a time and see if the allergy is triggered, thereby confirming what your cat is reacting to.

Treatment of Lysine Allergy in Cats

Should it be determined that your cat is experiencing an allergy to lysine, it is important to eliminate the supplement from your cat’s diet. If your cat has been exposed to the herpes virus and lysine has been helping to strengthen his immune system, your veterinarian may be able to recommend other supplements that can replace lysine.

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Recovery of Lysine Allergy in Cats

Once lysine is removed from your cat’s diet, the symptoms he is experiencing should resolve themselves. It is a good idea to work closely with your veterinarian to find other options that will help your cat strengthen his immune system. A strong immune system is particularly important if he has been exposed to the herpes virus as his immune system can keep the virus in check so that symptoms are not experienced.

Lysine Allergy Questions and Advice from Veterinary Professionals





4 Months and 9 months


10 found this helpful


10 found this helpful

My pet has the following symptoms:
I accidentally gave my cats 2 doses of lysine, 500mg per dose- 1000mg each cat in a day. Will they be ok?

July 23, 2020

Answered by Jessica N. DVM

10 Recommendations

Hello- Thank you for your question. The amount of lysine given should not be toxic for your cats. I would recommend skipping there dose this evening if you give it twice a day though. Monitor for G.I. upset and if you are concerned I would give your veterinarian a call.

July 23, 2020

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1 Year


10 found this helpful


10 found this helpful

My pet has the following symptoms:
Swollen Eyes
I found a stray kitten that was sick with goopy eyes clogged nose and respitory congestion. After keeping him separate from my other cat and nursing him back to health he got sick again and my other cat is experiencing symptoms but there kind of different. My adult cat has really swollen red eyes but not respitory stuff. What can I use to sooth her eyes

July 20, 2018

10 Recommendations

You should remove any gunk from the eyes from a warm damp cloth, flush the eyes out gently with sterile saline and apply an ophthalmic antibiotic ointment and monitor for improvement. Keep an eye on her for the time being and visit your Veterinarian if there is no improvement or symptoms get worse. Regards Dr Callum Turner DVM

July 21, 2018

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