Thumb sucking

Hey everyone,

So my son is about to be 14 months in the 1st of January and has been sucking his thumb since he was in the womb. It was ever really a problem until recently when his thumb started getting the way it is in the picture below.

Now his thumb is VERY dry red and basically chapped. I have no idea how to get him to stop or atleast stop it from getting worse ? He uses it as comfort when he’s upset or sleepy so of course I feel horrible when I try to stop him. HELP !