What term describes the toughening and hardening of the skin after tanning?

The term that accurately describes the toughening and hardening of the skin after tanning is indeed akinphosis. This physiological process occurs as the skin reacts to UV exposure, leading to a protective response that thickens the outer layer of the skin, primarily the epidermis. This thickening can enhance skin's barrier function and contributes to the appearance of a tan.

Keratinosis refers to the formation of keratin on the skin, which is somewhat related but does not specifically denote the process of hardening due to tanning. Dermatitis is an inflammation of the skin, often resulting from various irritants or allergens, and does not describe the hardening effect associated with tanning. Fibrosis pertains to the formation of excess fibrous connective tissue in an organ or tissue, which does not apply to the tanning process. Understanding these terms can clarify how the skin responds to tanning and the biological mechanisms at play.