Dark circles
So Wednesday was a long and draining day, followed by a long, late-night drive. I finally got to crash on the floor at 1:45am, only to be woken by 6:30am. Later in the day, what did I notice? Dark rings under my eyes…
What’s their deal? Well, they’re called dark circles, or sometimes periorbital dark circles. The prefix ‘peri’ means ‘about’ or ‘around’ (e.g. perimeter), and where the body is concerned, the orbit is the cavity or socket of the skull which contains the eye.
Most people associate dark circles with tiredness. There are other causes too, from allergies to the blood vessels around the eyes leaking a little blood to simply being genetically inclined to produce more melanin in the skin around the eyes (periorbital hyperpigmentation). But in my case I’m going with that first explanation - I was tired.
Let’s look at how being tired can affect your facial appearance.
The first thing to consider is that human blood is red. All the time. Oxygenated blood in the arteries is a nice bright red, whilst deoxygenated blood in the veins is a darker red. But still red. You may have noticed your veins, however, look bluish. This is simply because your skin and subcutaneous (under the skin) tissue allow blue light to pass through, but not so much other wavelengths/colours of light. So yes, your veins look blue.
The next point is that the skin under your eyes is relatively thin, about 0.5 mm compared to 2 mm for the rest of your body. Because the skin is thinner, it’s easier to see the blood vessels in this region.
Those two points explain why we get dark circles. They are simply the result of light reflecting off the blood vessels where the skin is relatively thin, leading to the dark blue appearance. But why would this be enhanced when you’re tired?
The answer to that is cortisol, a steroid hormone also known as hydrocortisone. Organic chemists will know it as 17α,21-dihydroxypregn-4-ene-3,11,20-trione (yes, that is all one word). A couple of its primary functions are to increase blood sugar through gluconeogenesis (the generation of glucose from non-carbohydrate carbon substrates) and to aid in the metabolism of fat, protein and carbohydrate. When the body is tired, production of cortisol is dramatically increased to give you the energy you need to stay awake. One of the things cortisol does is increase the volume of the blood in your body, which causes the body’s blood vessels to expand to allow for the extra blood. This, of course, includes the blood vessels under the eyes. Where the skin is thinner. Which means the extra blood is easier to see. Which looks dark blue. Which gives you dark circles.
Given some decent rest, this process reverses and you will notice the dark circles fade. I had a good sleep last night, and now my dark circles are much less apparent. Another good sleep tonight and I should be right.