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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.

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.

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

14 Years
Serious condition
1 found helpful
Serious condition

Has Symptoms

see above

Vet recommended Lysine for our cat and we started giving her a supplement - one treat a day, which was the lowest recommended dose. A few days later, she started having symptoms: face looks puffy, one eye seems almost swollen shut, loss of appetite, lethargic, not using litter box. Our other cat was taking it, too, and had no adverse affects. We're not sure if this is related to the Lysine (maybe she's allergic?) or if it's something else altogether. We stopped giving it to her. Does this sound like it could be an allergy? Thank you.

Dr. Callum Turner, DVM
Dr. Callum Turner, DVM
2499 Recommendations
Whilst an allergy to lysine itself is unlikely it is possible that Nala is allergic to something in the lysine treat; stop giving the treat and see if the symptoms decrease in severity, if the face is swollen and if there are any breathing difficulties visit your Veterinarian. Once the symptoms have resolved, you should try a different product to see if the symptoms recur. Regards Dr Callum Turner DVM

Thank you. We did stop the treats and are keeping an eye on her.

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4 Months
Fair condition
0 found helpful
Fair condition

Has Symptoms

Fur Loss
Bald spots

Medication Used

Lysine powder

How long will it take for my cat to get his fur back ive not given him the medicine for about 3 days now got the medicine on 12-9-2017 he wasnt taking it for about a week i gave him a few doses for the past few days but its not helping him so im not giving it to him anymore

Dr. Michele King, DVM
Dr. Michele King, DVM
1078 Recommendations
Thank you for your email. Lysine is typically given over a long term to help decrease the severity of upper respiratory viral diseases. If Buddy is having hair loss, he should be seen by your veterinarian for an examination, as in a kitten, common reasons for hair loss include parasites, fungal infections, and bacterial infections. He may need medications to treat his hair loss.

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