Which of the following conditions is associated with increased melanin production?

Increased melanin production is primarily a response to various stimuli, one of the most notable being sun exposure. When skin is exposed to ultraviolet (UV) rays from the sun, melanocytes, the cells responsible for producing melanin, increase their activity in an effort to protect the skin from UV damage. This enhanced melanin production leads to a darker pigmentation of the skin, commonly known as a tan.

The other choices refer to conditions or factors that either impede melanin production or result in a loss of pigmentation. Albinism and vitiligo are characterized by decreased or absent melanin. Albinism results from a genetic defect that affects melanin production entirely, while vitiligo involves the destruction of melanocytes, leading to patches of lighter skin. Psoriasis is a skin disease that is not directly related to increased melanin production but rather involves rapid skin turnover and inflammation, which can lead to discoloration and scaling without increasing melanin levels.

Thus, sun exposure is a well-established factor that triggers the body's natural mechanism to produce more melanin as a protective measure, making it the correct choice in this context.