i don't know about Seborrheic Dermatitis , but i definitely have atopic dermatitis. as well as dandruff. i have Really allergic skin, and having put all kinds of junk on my lips that i wasn't aware i was allergic to (Various kinds of moisturizers, chapsticks, lipsticks, corticosteroids, etc.), i developed EC. remember, i also have dermographism. could all be related.
HOWEVER...
i found something that works Really well for my lips. (unfortunately, i can't reverse my allergic skin.) i'll write about it as a response to cureforcurezone, check the more recent threads above this one!