What's wrong with Tommy's tail

Guys,
I've just noticed that the very tip of Tommy's tail has lost some fur and the skin appears very white and scaley. The attached photo isn't great but I am wondering what it might be. Any ideas?

Have you noticed him chasing it or nipping at it? Does he wag it ridiculously much?

It looks like he's maybe been chewing at it - does he chase his tail?

Yes, he does chase his tail when excited. I have a plastic bottle full of stones which I shake near him when I catch him chasing it. It's a habit he's had since being about 4 months old. I can't seem to break it though

I'd say he regularly catches it, then. He's worn the fur off, and exposed the bony tip.

I'd keep distracting him whenever you see him doing it. Maybe you could rub a little Vicks on it to put him off of biting it?

Ok, thank you. Vicks vapour rub it is then

Also, throw the bottle away. It is not advisable to shake things at them it might make them nervous.