And as a practical matter, it doesn't really clarify the pronunciation of Nguyen unless one knows which English pronunciation of ng you're referring to. I'm just teasing with this pedantry, of course; I understood what you meant. But then, I already knew how to pronounce Nguyen.
What are bruises? Bruises are bluish or purple-coloured patches that appear on the skin when tiny blood vessels, called capillaries, break or burst underneath. The blood from the capillaries leaks into the soft tissue under your skin, causing the discolouration.
What causes elbows, knees and certain areas of body skin to darken? One of the most common causes of darkened skin in these areas is contact or photocontact dermatitis. Contact dermatitis occurs when the skin is irritated by its contact with irritants or allergens. Photocontact dermatitis occurs when those irritants are stimulated by light (many allergens, such as fragrances, dyes and preservatives, are also photo-allergens, which can react with light to cause darkening).