Final answer:
Hyperpigmentation is the darkening of certain areas of skin due to excessive melanin production, often triggered by sunburn or inflammation. It is a sign of certain conditions, such as Addison's disease, and contrasts with depigmentation found in vitiligo. Exposure to UV radiation without protection can lead to DNA damage and skin cancer.
Step-by-step explanation:
Hyperpigmentation is a condition in which patches of skin become darker in color than the normal surrounding skin. This darkening occurs when an excess of melanin, the brown pigment that produces normal skin color, forms deposits in the skin. Hyperpigmentation can be caused by several factors including sun exposure, inflammation, or other skin injuries, including those related to acne vulgaris.
People with darker skin tones are more prone to hyperpigmentation, particularly with excess sun exposure. Sunburn is often a precursor to hyperpigmentation, as it is caused by large exposures to UV-B and UV-C radiation; this can increase the risk of skin cancer due to DNA mutations. The tanning response, which is a natural protective mechanism, involves the production of melanin pigments to absorb future UV radiation and protect living skin cells underneath.
Addison's disease is one example of an illness where hyperpigmentation is a characteristic sign, as depicted in the provided figures. In contrast, vitiligo is a condition where depigmentation occurs, leading to lighter-colored patches of skin. Moreover, conditions like xeroderma pigmentosum result in a failure to repair DNA damage from UV exposure, leading to skin lesions.