There are two reasons for dark knees. These reasons are not one or the other—both are responsible for dark knees.
Reason 1 – Rough skin
The skin in the knee area can become rough quickly, giving it a dull appearance.
The roughness does not cause darkness in the knee area. Roughness and darkness are two different issues in this area. Reason 2 (below) explains why the area can get dark.
Roughness accentuates the darkness. It makes the darkness more visible.
But why does the knee region become rough?
The roughness is primarily due to an excess number of old stubborn cells in the area.
Let me explain: Old cells on the skin’s surface have to fall off regularly to make way for younger cells from deeper layers. But some of these old cells are stubborn. They refuse to fall off. All these stubborn cells stick together and form a thin layer on the skin’s surface. This thin layer gives the skin a very dull look.
This layer of old cells is much more pronounced in the knee area, giving the area a very visible rough feel.
Buy why is it more pronounced in the knee area? The skin in the knee area has fewer sebaceous glands, which means less sebum (oil) on the skin. Sebum keeps skin moisturised. Since the amount of sebum is less in the knee area, the skin tends to dry much more quickly.
In dry skin, more old cells become stubborn (don’t fall off easily), and fewer younger cells travel upwards to replace the old cells. This means there are many more old cells, resulting in a thick, rough layer on the skin’s surface.
The rough layer makes any darkness on the knee area much more pronounced.
But why is there darkness in the knee area in the first place? Reason 2 explains.
Reason 2 – Dark skin
Knees are a high-impact area.
There is a lot of friction in the knees because of what our knees do (help us with bending, walking and running).
All this friction can irritate the skin. The knee area has folds. These folds further increase the irritation.
Irritation can lead to an overproduction of a pigment called melanin in the deeper layers of the skin. The excess melanin travels upwards and reaches the top layer of the skin.
Melanin is dark in colour. Because melanin is dark, the portions of skin with excess melanin become dark. This portion of skin that is darker than the surrounding is called pigmentation.
Because the knee area is so irritated, there is usually an overproduction of melanin, which results in dark knees. It is important to note that this irritation on the skin is not often visible.
The darker your overall skin colour, the higher the chances of irritation leading to an overproduction of melanin. This is why pigmentation is a bigger issue for people of colour, and dark knees are much more common.