puupy has a swollen white spot on his tail

I have a chocolate lab who is 4 months old. I large spot on his tail is starting to turn white and its looks likes his tail is swelling a little at that same spot when he plays. When I touch it it doesn't seem to bother him at all.
I'm not sure what this is? Any advice would be much appreciated.

Could be an infection / a tick / a foreign body in their / damage to the skin / cut / whatever

Vet trip