Puss filled blister.

[Plumsofgold]

Yesterday dd2 had a smallish blister on the end of her thumb, this morning she has woken up and it has got a lot bigger.

Any idea what it could be?

It sounds like a whitlow or felon. See a pharmacist. You can get magnesium sulphate a drawing paste to put on it.

Googirl sucked her thumb so much she got an infected blister. It popped in the bath and healed perfectly.