What Makes The Skin Around The Mouth To Go Pale On Waking Up?

My 15-year old daughter is "white around the mouth" or pale every morning when she gets up. After a few hours she sometimes gets her coloring back, but oftentimes remains pale around her mouth up in the day. She doesn't really feel bad, but I do know she is very thin. She's 5-10 and weighs 110 which is not uncommon in my family--I was very underweight growing up. I was wondering if this was a deficiency of some type.