Lip blister/suck blister

Looking to see if anyone else has experience with this. My LO is 21 months. Hasn't breastfed or had bottle/pacifier since he was 1 year old. He currently drinks out of straw cups, open cups, and the munchkin 360 cups. He still every now and then gets a lip blister (usually called a suck blister) right in the middle of the top lip. Typically it's never really a blister like but ends up having a little piece of skin dry and peel off. With the cold weather it seems to be getting really dry. Doesn't bother him other than when the skin is loose. Something to worry about or something they just grow out of?