It is important for the epidermis to be efficient in protecting the body from UV radiation. Why is it also important for the epidermis to not be too efficient in doing so.

High concentrations of UV radiation can be damaging to the skin, but low concentrations are beneficial to the body. One major benefit of low UV radiation concentration is conversion of 7-dehydrocholesterol to vitamin D3, which travels from the skin to the kidney and liver for activation to vitamin D. Vitamin D is essential for various body functions like raising calcium levels in the blood that also helps in bone growth and formation. Therefore, it is not important for the epidermis to be too efficient in blocking UV radiation.

Explanation

The skin is made up of three main layers; the epidermis which has dead cells, the dermis, and the subcutaneous fat layer. The part that is directly exposed to the sun is the epidermis, which protects the other layers and cells of the body from potential damage by UV radiation from the sun. The same UV radiation plays an important role in making vitamin D that is used by the body in bone growth and maintaining calcium levels.