Which layer of the skin thickens during the tanning process?

During the tanning process, the layer of the skin that thickens is known as the horny layer, or the stratum corneum. This layer is the outermost section of the epidermis and is primarily composed of dead skin cells that have become keratinized. When exposed to ultraviolet (UV) light, the skin responds by increasing the production of melanin, which leads to a darker skin tone. This protective mechanism also results in the thickening of the horny layer, as the skin builds up to safeguard itself from further UV damage.

The thickening of this layer plays a crucial role in the body's defense against UV radiation; it acts as a barrier and can help to reduce the penetration of UV rays into the deeper layers of the skin. In contrast, the dermis, which lies beneath the epidermis, consists mainly of connective tissue and does not thicken in response to tanning. The subcutaneous layer, also known as the hypodermis, is composed mainly of fatty tissues and provides insulation and cushioning but does not thicken as a result of tanning. The basal layer, the deepest part of the epidermis, is responsible for the production of new skin cells but does not significantly change in thickness during the tanning process.