I've always wondered: why do we get dark circles under our eyes?

Many people have an appearance of dark circles on the lower eyelids, and they have many different causes.

That creepy eye on the back of the dollar bill, explained

How to Get Rid of Dark Circles Under Your Eyes

I've always wondered – News, Research and Analysis – The Conversation – page 1

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Why is my left under-eye circle darker than my right? - Quora

Mesotherapy Under Eyes Review: What To Expect From The Treatment

Dark under eyes that are progressively getting worse (30M) : r

CeraVe Eye Cream for Wrinkles, Under Eye Cream with Caffeine, Peptides, Hyaluronic Acid, Niacinamide, and Ceramides for Fine Lines, Fragrance Free & Ophthalmologist Tested

I've Always Wondered: Why Do We Get Dark Circles Under Our Eyes