yeah puncturing it can cause infections fast! It's kind of his body's defense - you know how when you wear new shoes, you get a blister? That is your body defending itself - it's a way to cushion, and protect, and usually leaves a callus that then helps you continue to wear those shoes :) hence why flip-flop wearers have stronger skin between their toes!! And those that puncture it, tend to have more pain and a longer time for it to heal. Epsom salt for us, works for that.
Epsom salt for them, works for that :p
If it doesn't work we may need to ask about it being a cyst, tumor, etc... I don't want you being alarmed, but it is possible and not uncommon. You can meet many of us who've had tumor bettas and we can help you with it!