Hyperpigmentation is a condition characterized by darkening of the skin, typically caused by an excess production of melanin. The most common causes of hyperpigmentation include:

1. Sun Exposure: Ultraviolet (UV) radiation from the sun stimulates melanin production as a natural defense mechanism, leading to sunspots or age spots.
2. Inflammation: Post-inflammatory hyperpigmentation (PIH) occurs after skin injury or inflammation, such as acne, eczema, or psoriasis. The affected area becomes darker as it heals.
3. Hormonal Changes: Conditions like melasma are often triggered by hormonal changes, particularly in pregnant women (often called “the mask of pregnancy”) or those taking oral contraceptives or hormone replacement therapy.
4. Medications: Certain medications, such as some chemotherapy drugs, antibiotics (like tetracyclines), and non-steroidal anti-inflammatory drugs (NSAIDs), can cause hyperpigmentation as a side effect.
5. Medical Conditions: Diseases such as Addison’s disease and hemochromatosis can cause hyperpigmentation. Addison’s disease leads to increased production of melanin, while hemochromatosis involves excess iron deposits in the skin.
6. Genetic Factors: Some individuals are genetically predisposed to develop hyperpigmentation, with a higher prevalence among those with darker skin tones.
7. Exposure to Certain Chemicals: Contact with certain chemicals, such as some cosmetics, perfumes, or even skin care products, can lead to hyperpigmentation.
8. Aging: As people age, their skin may produce more melanin in response to sun exposure and other factors, resulting in age spots.

Each of these causes can lead to different patterns and types of hyperpigmentation, and effective treatment often requires addressing the underlying cause.