While your skin is made of three layers including the subcutis and the dermis, hot showers affect the outermost layer, the epidermis. The epidermis is mostly composed of skin cells loaded with keratin, the same substance that makes up your hair and nails. These cells, called keratinocytes, not only provide a tough defense against the environment but also help your skin to retain moisture. To help keratinocytes retain the skin's moisture, your body produces a thin layer of oil. Together, the outermost layer of skin cells and oil comprise the stratum corneum, and it's this layer that takes a beating during a hot shower.