Blood blister on gum.

[MummyPig24]

Ds age 6 said his gum hurts and when I looked he has a blood blister on it right at the back. He still has 20 teeth so is this to do with more teeth coming through?

It is probably an 'eruption cyst'. When the first permanent molar is about to erupt the gum becomes very thin and the area looks very much like a blood blister. Within the next few days the tooth will erupt.