Looks like a local bacterial infection just under the first layer of skin. Probably from getting a slight injury just inside the nostril from a sharp piece of substrate or cage. And that just spread after becoming infected. Could be from mouthrot, but in most cases the infection would stay closer to the side of the head, bot to the top and front? But since it's so little that is still a possibility . . . I don't know if I'd give a snake that small any antibiotics, I've never had to make that decision, but if it got progressively worse, you might have to give it a very tiny, tiny dose. . . (I would need to check my records and my calculator for that one) If it does not get any bigger than what it is now, the snake will recover after it sheds. It will leave a nasty scar there, that will take many sheds to go away, but it will go away for the most part, especially since it's just a hatchling. Hopefully it won't get any worse than it already is. . . I wish you all the best,
Zee
-----
"I am an expert on everything, but I know so little and have so much to learn!" -Carsten "Zee" Zoldy-