Puffiness under just one eye usually comes from a localized trigger rather than a systemic problem. When both eyes are puffy, the cause is often something affecting your whole body, like allergies, poor sleep, or fluid retention. But when only one side swells, something specific is happening on that side: a blocked gland, a minor injury, an insect bite, an infection, or a reaction to something that touched that particular eye. Most causes are harmless and resolve on their own, but a few need prompt attention.
Styes and Chalazions
The most common reason for a bump or puffiness under one eye is a blocked oil gland in the eyelid. Your eyelids contain dozens of tiny glands that produce the oily layer of your tears. When one of these glands gets clogged, it can form either a stye or a chalazion, and either one can make the area underneath your eye look swollen.
A stye is an acute infection of the gland. It’s red, painful, and tender to touch, and it often looks like a small pimple near the lash line. A chalazion, by contrast, is a painless, firm lump within the middle of the eyelid that develops when a blocked gland becomes chronically inflamed rather than infected. It can press on surrounding tissue and create enough swelling to make the whole under-eye area look puffy, but the skin around it typically looks normal. Warm compresses applied for 10 to 15 minutes several times a day help both conditions drain and resolve.
Allergic Reactions and Contact Irritation
An allergic reaction can absolutely affect only one eye. If a particular cosmetic, eye cream, or sunscreen was applied unevenly, or if you rubbed one eye after touching an irritant, the reaction will show up on that side alone. Contact dermatitis around the eye is a delayed immune response to a chemical that binds to skin proteins. There’s often a two-to-five-day lag between the exposure and the onset of redness and swelling, which makes it tricky to identify the culprit.
Common triggers include new makeup, nail polish (transferred by touching your face), hair dye, fragrances, and preservatives in skincare products. Insect bites and contact with plants like poison ivy can also cause one-sided swelling. If you suspect an irritant, switch to fragrance-free products, avoid rubbing the area, and apply a cool compress to reduce swelling.
Sinus Infections
Your sinuses sit directly behind and below your eye sockets, separated by paper-thin bone. When a sinus infection develops on one side, the resulting inflammation and fluid buildup can push forward and cause visible puffiness under the eye on that same side. You’ll usually notice other symptoms too: nasal congestion that’s worse on one side, pressure in your cheek or forehead, and possibly a dull ache that worsens when you bend forward. This type of under-eye puffiness resolves once the sinus infection clears.
Blocked Tear Duct
Your tears normally drain from the inner corner of each eye through a small duct into your nasal passages. When that duct becomes blocked, tears pool and stagnate, and the tear sac near the inner corner of the eye can become inflamed or infected, a condition called dacryocystitis. This produces swelling concentrated near the inner lower part of the eye, along with tearing, redness, and sometimes discharge. It almost always affects one side. Blocked tear ducts are especially common in newborns but can happen in adults after a sinus infection, nasal injury, or as a result of aging.
Dental Infections
This is one that surprises people. An infection in an upper tooth, particularly the canines or premolars, can spread upward into the cheek and eye area. The roots of your upper teeth sit very close to the maxillary sinus, and the thin bone separating them allows infection to travel. The tissue around and below the eye has no lymphatic drainage and its veins lack valves, meaning infection can extend into the area with little resistance. If you have under-eye swelling along with a toothache, facial tenderness, or a history of dental problems, the two may be connected.
Injury or Trauma
Even a minor bump to the face can cause fluid to collect under one eye. A more significant blow, like being hit by a ball or an elbow during sports, can fracture the thin floor of the eye socket (called a blowout fracture). Symptoms include swelling under the eye, bruising, and sometimes numbness in the cheek. If you took a hit to the face and notice that the swelling isn’t improving after a day or two, or you’re having double vision, that warrants medical imaging to check for a fracture.
Periorbital Cellulitis
Periorbital cellulitis is a bacterial infection of the eyelid or the skin surrounding the eye. It typically starts after a scratch, insect bite, or small wound near the eye allows bacteria to enter, or it can spread from a nearby sinus infection. The affected eyelid becomes red, swollen, warm, and tender. Vision and eye movement remain normal because the infection stays in front of the eye socket, not behind it. It’s more common in children and usually responds well to oral antibiotics.
When Swelling Signals Something Serious
Most causes of one-sided under-eye puffiness are benign, but a few warning signs point to something that needs urgent care. Orbital cellulitis is a deeper infection that spreads behind the eye into the socket itself. Unlike the surface-level version, it causes the eye to bulge forward, pain when moving the eye, changes in vision, and fever. If you or your child develops a combination of these symptoms, especially a bulging eye with fever, that’s an emergency room situation. Untreated orbital cellulitis can damage vision permanently or allow infection to spread to the brain.
Other red flags include swelling that gets rapidly worse over hours, severe pain that doesn’t respond to over-the-counter pain relievers, and any change in your ability to see clearly or move your eye normally.
Simple Steps to Reduce the Swelling
For garden-variety puffiness, a cool compress is the most effective first step. Soak a clean washcloth in cold water and lay it over the eye for five to ten minutes. The cold constricts blood vessels and reduces fluid buildup. Chilled cucumber slices, refrigerated tea bags, or even a cold spoon work on the same principle. Elevating your head with an extra pillow while sleeping helps prevent fluid from pooling overnight.
Warm compresses are better when the cause is a blocked gland (stye or chalazion) because the heat helps soften the clogged oil and encourage drainage. If you’re unsure which approach to use, consider the nature of the swelling: a defined bump in the eyelid benefits from warmth, while general puffiness or swelling from a bite or irritant responds better to cold. If the swelling doesn’t improve within a few days, gets worse, or is accompanied by pain, fever, or vision changes, it’s worth having a doctor take a look.