Dark circles under the eyes are caused by a combination of thin skin, visible blood vessels, pigmentation, and structural changes in the face. The skin beneath your lower eyelid is only about 1.0 to 1.4 millimeters thick in younger adults, making it one of the thinnest areas on your body. That thinness means anything happening just beneath the surface, from pooling blood to shifting fat pads, shows through more easily than it would anywhere else on your face.
Why Under-Eye Skin Shows Everything
The lower eyelid has very little subcutaneous fat compared to the rest of your face. Blood vessels sit close to the surface, and when blood pools or moves sluggishly through those vessels, the area takes on a blue, purple, or brownish tint depending on your skin tone. Think of it like looking at veins on the inside of your wrist: the darker the blood beneath, the more visible it becomes through pale, thin tissue.
As you age, this skin gets paradoxically thicker (measuring around 2.0 mm by your 50s) but loses elasticity and structural support underneath. The result is skin that creases, sags, and casts shadows rather than lying taut over the bone. So while the skin itself may technically gain tissue, the overall appearance worsens because the architecture beneath it deteriorates.
Genetics and Skin Tone
Family history is one of the strongest predictors. In clinical studies, about 53% of people with persistent dark circles had a family member with the same issue. A separate analysis found genetic predisposition in roughly a third of all patients. If your parents had dark circles, you’re more likely to develop them regardless of how much sleep you get or how well you take care of your skin.
Prevalence is also higher in people with darker skin tones. This is partly because darker skin produces more melanin around the eyes, and partly because the contrast between the orbital area and the surrounding skin can be more pronounced. Researchers have even identified specific gene variants linked to both the vascular and pigmented types of under-eye darkening, suggesting that some people are simply wired to deposit more pigment or develop more prominent blood vessels in this area.
Sleep Deprivation and Blood Flow
Poor sleep doesn’t just make you feel tired. It changes how blood moves through your face. Research on the biophysical effects of sleep deprivation found that blood flow beneath the eyes decreases significantly after poor sleep. When blood moves sluggishly through the tiny vessels under your lower lids, it pools and becomes more visible through the thin skin. This stagnation is a direct contributor to the dark, bruised look many people notice after a rough night.
Sleep deprivation also makes your skin paler overall, which increases the contrast between the under-eye area and the rest of your face. The combination of slower blood flow and lighter surrounding skin makes dark circles look dramatically worse, even after just one or two nights of poor rest. The good news is that this type of darkening reverses relatively quickly once you return to a normal sleep pattern.
Allergies and Nasal Congestion
Allergies cause dark circles through a mechanism that has nothing to do with rubbing your eyes, though that doesn’t help either. When your immune system reacts to allergens, the moist lining inside your nose swells. That swelling compresses the veins that drain blood from the area around your sinuses, and those veins happen to run directly beneath the skin under your eyes. When they swell with backed-up blood, the area looks darker and puffier. Doctors sometimes call these “allergic shiners.”
Any type of chronic nasal congestion can trigger the same effect, whether it’s from seasonal allergies, a sinus infection, or a deviated septum. The darkening tends to affect both eyes equally and often comes with visible puffiness. If your dark circles get worse during allergy season or when you have a cold, congestion is likely a major contributor.
Aging and Structural Changes
One of the most common causes of worsening dark circles with age has nothing to do with pigment or blood vessels. It’s about volume loss. Your face contains fat pads that sit beneath the eye socket muscles and along the upper cheek, giving the area a smooth, full appearance when you’re younger. Over time, the ligaments holding those fat pads in place weaken, and the fat itself shrinks. The result is a visible groove between your lower eyelid and your cheek, sometimes called a tear trough.
This groove creates a shadow that looks like a dark circle even in perfectly even lighting. The effect worsens as the underlying bone gradually resorbs with age, deepening the hollow further. This is why some people in their 40s and 50s develop dark circles for the first time despite never having had them before. It’s not discoloration at all; it’s a shadow cast by changing facial structure. Treatments for this type focus on restoring volume rather than lightening pigment, which is an important distinction if you’re trying to address the issue.
Diet, Salt, and Fluid Retention
A high-salt diet causes your body to retain fluid, and the loose, thin tissue under the eyes is one of the first places that extra fluid accumulates. The swelling creates puffiness that casts shadows and stretches the skin, making underlying blood vessels more visible. You might notice this after eating a particularly salty meal the night before, waking up with eyes that look swollen and dark.
Alcohol and dehydration work through a related pathway. Alcohol dilates blood vessels and disrupts fluid balance, while dehydration causes the skin to look more sunken and translucent. Both make the under-eye area appear darker. Reducing salt intake and staying well-hydrated won’t eliminate dark circles caused by genetics or aging, but they can meaningfully reduce the puffiness and shadowing that make existing circles look worse.
Iron Deficiency and Other Medical Causes
Iron-deficiency anemia reduces the oxygen carried in your blood, giving it a darker appearance that shows through the thin under-eye skin. If your dark circles appeared suddenly or worsened alongside fatigue, pale skin, or shortness of breath, low iron levels could be involved. A simple blood test can confirm or rule this out.
Thyroid disorders, eczema (particularly atopic dermatitis affecting the face), and certain medications can also contribute. Eczema around the eyes leads to chronic rubbing and scratching, which over time increases pigment deposition in the skin. This post-inflammatory hyperpigmentation creates a brownish discoloration that persists even after the eczema flare clears.
Sun Exposure and Pigmentation
Ultraviolet light stimulates melanin production, and because the under-eye skin is so thin, even modest sun exposure can trigger visible darkening. This is especially true for people with naturally higher melanin levels, where sun exposure amplifies an already active pigment pathway. The darkening from UV tends to appear brownish rather than blue or purple, which can help distinguish it from vascular causes.
Wearing sunscreen on the under-eye area and using sunglasses with adequate coverage can slow this process. Unlike the vascular or structural causes, pigment-driven dark circles respond to topical ingredients like vitamin C and retinoids, which gradually reduce melanin deposits over months of consistent use.