It is difficult to make a diagnosis without examination, but some possibilities are there. First, it can be due to atopic dermatitis.
Second,it can be pityrisis versicolor. This is characterized by hypopigmented, round to oval, scaling patches on the upper arms, neck, or shoulders.
Thirdly,it can be vitiligo.It is a pigmentation disorder in which melanocytes (the cells that make pigment) in the skin are destroyed. As a result, white patches appear on the skin in different parts of the body.
Treatment is different for all three.So I feel that an evaluation by a dermatologist will help in confirming a diagnosis.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Thank you so much about your information.