What Causes Small Dandruff Patches On The Head And Hair Loss?

Hi my daughter is 13, she is about 1.47m, and around 38kg. She has asthma, excema, and lots of allergies. Now she has developed white patches on her head, there are bits like dandruff on her head and then in the morning there is no hair there. It's small patches but they are all over her head. And now she feels slightly weak and ill. What can i do. Please help