Final answer:
The subject concerns skin conditions like vitiligo, which causes lighter patches on the skin, and melanoma, which appears as irregular brown or black patches. Both have significant implications for health and treatment.
Step-by-step explanation:
The question is related to skin conditions, which can be manifested as changes in pigmentation and texture. Vitiligo is one such condition, where individuals experience depigmentation, resulting in lighter colored patches of skin. This condition is particularly noticeable on darker skin. Another serious condition is melanoma, which presents as large brown or black patches with uneven borders and may have a raised surface. Both conditions require attention from medical professionals; vitiligo for cosmetic and psychological concerns and, more critically, melanoma for its potential as a life-threatening skin cancer.
Other skin issues mentioned include signs of psoriasis, characterized by itchy or sore patches of thick, red skin with silvery scales; Addison's disease, which may cause hyperpigmentation, and various infections and inflammatory conditions that can affect the skin's appearance and function.