Why is 13 year old sons arm more hairy after having it in plaster for six weeks was broken and cast removed?

It is a common misconception that hair growth increases after an arm has been in a cast. When a cast is removed after a period of time, it is normal for the skin underneath to appear paler and softer than the surrounding skin. This is because the skin has been protected from the sun and other elements, and has not been exposed to the same level of wear and tear as the rest of the body. Therefore, any existing hairs on the arm will appear darker and more noticeable in comparison, causing the false impression of increased hair growth.