I found this spot on my 7 week old kitten, seems not painful, I tried to clean it using H2O2 it gone but 5 days later appeared again with new spot on noise. Is it an infection? Should I go to vet?
My immediate guess was freckles. Really. Orange tabbies have freckles under their fur. Surprised me too when I first noticed on mine, but it's entirely normal.
If it's really something that can be cleaned off, it could be something greasy that the cat is rubbing against, or...
Basic principle: if you are asking "should I go to the doctor/vet", you should. (I spent 24 hours walking around with an atypical heart attack in progress. Don't Do That.)
The vet said it is feline acne, most likely cause by using plastic plate, it is a kind of allergic reaction to plastic, and my kitten was too small to clean itself properly. The best remedy is to dry it with H2O2 hydrogen peroxide multiple times during 5 mins the when it becomes soft try to clean with dry cotton, don't scratch the spot. Repeat the process next day utill you remove the spot, and switch to metalic plate.