I had a friend growing up that had a bump on his forehead. We would all make fun of him because it was hard. You'd actually would have to stare at him to notice it, it was that small. The skin had never been broken so his horn was never really exposed. It was just a little bump.
He never even had it checked by a doctor to see what it was. To him it was just his skull, but it could have been a Cutaneous Horn? Maybe! They haven't found a cause for a Cutaneous Horn, but radiation exposure is believed to be the cause. They've been known to grow from burn scars, which explains the frequency of cases in Japan after Hiroshima. People looked when they should have ducked and rolled. They've even found a link to HPV-2 virus.
The friend with the horn has long passed, not from his horn but naturally of a heart attack, so his secret has gone to the grave with him. No one will ever know if he really had a horn or not.
For him it might have stayed hidden under his skin but usually around the age of 70 or 80 they break through, exposing themselves. He never had to deal with it.
I imagined my friend with a horn growing out of his forehead, near the centre, just above his uni-brow, poking through his skin. It could actually be a benign keratinous skin tumor, rarely are they malignant, which has the appearance of a horn, and sometimes looks like a piece of dried-out wood or coral, which keeps growing.
So, this is very important to remember. During a nuclear attack, don't stop to look out the window to see what's happening, you could start to grow a horn when everything has settled down. Duck roll and cover, like they taught us to do in every school room, in the fifties.
But, say you just couldn't help it and had to look. You walked right up to the window and gawked as the radiation wave hit you. Years later you started growing a horn. Do not worry!
It can always be clipped down to a stub with finger nail clips and a good file. Or, you can let it grow and saw it off like a branch of a tree. It's made from the same material your finger nails are and as a last resort it could be easily surgically removed. There is one thing stranger thing about it though, it keeps coming back.
Now-a-days, they probably don't bother to teach the kids to; Duck, roll and cover, preferring the alternative.
Yikes! A class room full of little devils.