When I see those types of lesions in young cats, I make a mental list of possible causes. Very rarely is a skin condition 'bad', but if it is spreading then it's time to check it out.
I would be suspicious of ringworm (actually a fungal infection). Cats also have allergies, and if so, can break with lesions like this from self induced scratching. Either way I would have your vet do an exam, in most circumstances the lesions can be treated effectively and life goes on. Thanks.