Dark patches on the face in a 45-year-old woman are most commonly due to conditions like melasma, sun-related pigmentation, or post-inflammatory pigmentation, and the treatment depends on the exact cause. The most important step is strict sun protection using a good sunscreen every day, wearing a scarf or hat outdoors, and avoiding direct sun exposure as much as possible, because the sun is the main trigger for worsening pigmentation. Topical treatments prescribed by a dermatologist, such as depigmenting creams (for example, combinations containing hydroquinone, retinoids, or azelaic acid), can gradually lighten the patches when used correctly. Chemical peels or laser treatments may also be options in stubborn cases under specialist care. It is also helpful to check for contributing factors like hormonal changes or thyroid issues if pigmentation is widespread or worsening. Since many treatments need supervision, it is best to consult a dermatologist for proper diagnosis and a safe, tailored treatment plan.