Child Having White Patches On Knees And Elbows. No Itching. Advice?

Hi, I have a 4 years old daughter who have white irregular shape patches on both knees and elbows, when it started was only on one of the knees, but they are spreading and getting bigger, started like the size of a coin and now it covers the whole knee and elbow...It looks like dry skin when scracthed, but without scratching the area. Is not itchy or raised, lotion helps on getting rid of the white color but she is kind of tan color skin and even with lotion it can be seen the affected area slighly lighter color than the rest... Any reason or recomendation ?