What Causes Raw, Cracked And Peeling Lips?

For 6 mos., have had recurring problem with lips getting raw - then they crack & peel. One time they even swelled a bit so went to dermatologist who said "probable allergic reaction" & gave me steroid cream that does clear it up. Have not been able to figure out WHAT I'm allergic to. Thought for awhile it might be citrus, then possibly sulfites in wine.... or maybe citric acid(?). Last week, had a recurrence when I'd had no citrus for weeks & no alcohol in over a week but I did take an Emergen-C (vitamin powder packet). Seemed to flareup within an hour or two after that. Another time, it seemed to occur the morning after I had eaten a lot of raw blueberries the night before. I eat a fairly healthy diet, am normal weight, have no indigestion/reflux problems that I'm aware of. I am on medication for hypothyroidism & take a number of vitamin supplements. Any insight? Thank you.