Toddler keeps licking under bottom lip

I don't know if this is becoming just a habit, or if there is some kind of problem causing it, but my toddler (2 years, 9 months) keeps using his tongue to lick under his bottom lip, so the top of his chin. He has done this for a while, mostly we thought it was because when he had a dummy he would dribble a bit. But recently he gave up the dummies and now i am noticing him doing it more than ever. I don't know if its just a habit or why he would do it. He's now getting a bit red there, like when you wipe your nose too much. I have started telling him not to do it, but he forgets and does it again. I was thinking maybe of putting something there, like vaseline to disencourage him, but was also thinking i probably should figure out first why he is doing it and try to stop it that way. I asked him but he doesn't know.

Has anyone else had this happen?

id say its partly habit partly annoying now for him, its probably dry and uncomfy so he licks it which makes it feel better for a while before it annoys him again so a never ending cycle, try putting pawpaw cream om it to promote some healing, not sure what else to try

Thanks! he's now saying its sore, which would be from him keeping doing it. I haven't got any pawpaw here now, what about calendula?

id say that would be fine!!! its a vicious cycle poor thing