Why brows turn red?

The reason why brows "turn red" is not solely a matter of the number of iron oxide particles in the skin, which is often the cause of a bluish color when it comes to carbon particles. While the issue with carbon black is largely a physical, and more specifically optical, phenomenon, the "red" pigment issue is more related to biochemistry. Essentially, it's due to the modification of iron oxides within the skin over time. The potential for a reddish hue is linked to two specific iron oxidesFe2O3 (Hematite - Red Iron Oxide - CI 77491) and Fe3O4 (Magnetite - Black...