Hi, My 4 year old son has developed some white patches on both his elbows one month ago ( refer the picture) which now also started developing on one of his knees. We live in Germany and the doctor said she is not familiar with dark skin conditions/reactions. We used good moisturer and oats lipids ceramide lotion(dermexa aveeno eczema cream) too. Nothing is working. Is this a vitamin deficiency or some other skin condition. Please suggest what to use.