My 10yr old daughter also has this strange "musty" odor in her hair not sure if its her scalp - hours after a shampoo the smell returms. I have washed her linens, hats etc. I have tried all different shampoos. Her scalp looks clear no flaking, or anything though she soes have Keratosis which seems to be genetic. She has straight, light brown long hair which she usually wears in a pony tail. She isnt heavy - only 62 lbs. She runs a high body temperature and is always hot she would prefer to wear shorts and t-shirt in the middle of winter! I think maybe it has something to do with her sweat, she showers at least every other day. She uses deodorant since 8yrs old. I dont know what else to do as I havent heard of this before.