Hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin production. Melanin protects us from the effects of strong sunlight but often due to a variety of different influences such as UV or trauma leads to inflammation at a cellular level which causes the skin to produce more melanin. This results in darker skin spots or areas, such as age, liver and sun spots, after local damage from acne or burns, or pregnancy mask (often seen post pregnancy on the jaw line and other facial areas).
The body attempts to resist over production but with continued exposure and with aging then over exposed skin can lose its ability to restrict over production and lead to long term hyper pigmentation marks. During times of hormonal variation such as being pregnant then the control of pigment production can be diminished and this also can lead to hyper pigmentation.