Hello I have just recognized a problem on my cats lip. Seems as the one in the article I have seen

It is difficult to tell form the picture alone what is going on with your cat's lips unfortunately. It almost looks like she/he has a sore or even infection in her/his whiskers and commissure of the mouth. I would recommend you take your cat to your vet for an exam. She/he may need antibiotics to resolve this and possibly pain medication is she/he is is uncomfortable. I would also be concerned there may be sores in the mouth that need to be addressed if you are seeing them along the outside. It is possible your cat licked something toxic or caustic causing these problems. I would look around your home to see if there is anything she/he could have gotten in to. I hope your cat improves quickly!

Your cat is suffering from rodent ulcers. This is an inflammatory reaction caused by the immune system. It is usually related to an underlying allergy. I would recommend taking your cat to the vet to be examined. Common treatments include immune modulating drugs, like steroids or cyclosporine, antibiotics to prevent the infection from getting worse, and a hypoallergenic diet. It is also important that your cat be on flea medication because a flea allergy can contribute to this as well. This condition can usually be well controlled with medication and diet change. The most important thing is getting it treated soon before becomes any worse. I hope this helps. Thanks for using Petco Pet Education Center, formerly Petcoach. Best of luck.