A red and swollen eye on one side can be a distressing symptom, often accompanied by discomfort, visual disturbance, or even pain. While it may seem like a minor irritation at first, such symptoms can signal various underlying conditions—ranging from simple allergies to serious infections or inflammatory eye diseases. Recognizing the cause and receiving the correct treatment is essential to prevent complications and protect your vision.
Allergies are a frequent cause of redness and swelling in one eye. Triggers may include pollen, dust, pet dander, or contact with certain eye drops or cosmetics. Allergic conjunctivitis may cause:
Itching
Tearing
Mild swelling
Redness in one or both eyes (though sometimes just one)
Eye infections are another leading cause and can affect one eye more severely than the other. Types of infections include:
Bacterial Conjunctivitis
Usually starts in one eye and may spread. Symptoms include yellow or green discharge, redness, and eyelid swelling.
Viral Conjunctivitis
Often starts in one eye with watery discharge and may follow a respiratory infection.
Stye (Hordeolum)
An infected oil gland on the eyelid causes a painful, red lump that can lead to localized swelling.
Preseptal (Periorbital) Cellulitis
An infection of the eyelid and surrounding skin that causes significant swelling, redness, and warmth.
Orbital Cellulitis
A severe, potentially vision-threatening infection behind the eye. Symptoms include painful swelling, fever, difficulty moving the eye, and visual disturbances.
Blepharitis
Chronic inflammation of the eyelid margin, causing red, swollen, and itchy eyelids. It typically affects both eyes but can begin on one side.
Episcleritis or Scleritis
These are inflammatory conditions of the white part of the eye, leading to redness and swelling. Scleritis may cause deep pain and is often associated with autoimmune diseases.
A small object lodged in the eye or trauma to the area can lead to unilateral redness and swelling. This can include:
Dust or sand
Insect bites near the eye
Accidental scratches
Post-surgical swelling
Improper use or cleaning of contact lenses can lead to irritation or infection in one eye, causing redness, pain, and swelling. Giant papillary conjunctivitis (GPC) may also develop from prolonged lens use.
If you experience any of the following, seek immediate medical attention:
Sudden and severe swelling or pain
Vision changes (blurring, double vision, vision loss)
Eye movement problems
Fever or general malaise
Yellow or green discharge
Recent trauma to the eye
Prompt diagnosis can prevent permanent damage and identify systemic diseases early.
At Bangkok Eye Hospital, our team of board-certified ophthalmologists and oculoplastic surgeons specialize in the diagnosis and treatment of complex eye conditions. The diagnostic process includes:
Comprehensive eye examination
Slit-lamp biomicroscopy
Fluorescein staining to detect corneal abrasions
Culture or swab for suspected infections
Imaging (e.g., CT scan or ultrasound) in case of suspected orbital cellulitis or trauma
Treatment depends on the root cause. Our specialists tailor each treatment plan according to the patient's symptoms and medical history.
Antibiotics or antiviral eye drops for infections
Antihistamines or corticosteroid drops for allergies and inflammation
Lubricating eye drops for relief in irritation or dry eyes
Oral medications for severe infections or systemic involvement
Incision and drainage of styes or abscesses
Foreign body removal under sterile conditions
Lacrimal surgery if tear duct blockage is the issue
Oculoplastic procedures for recurrent swelling or structural issues
Warm or cold compresses to relieve symptoms
Proper eyelid hygiene for chronic conditions like blepharitis
Adjusting or stopping contact lens use if they’re a contributing factor
Wash hands before touching your eyes
Avoid sharing towels, eye drops, or cosmetics
Clean contact lenses properly and avoid extended wear
Use protective eyewear during outdoor or hazardous work
Schedule regular eye check-ups, especially if you have allergies or chronic eye conditions
At Bangkok Eye Hospital, we offer a wide range of services tailored to manage and prevent red and swollen eye conditions:
General Ophthalmology Clinic: For diagnosis and treatment of eye redness, infections, and inflammation
Oculoplastic and Orbital Surgery Clinic: Specialized care for styes, eyelid disorders, and orbital cellulitis
Allergy & Dry Eye Clinic: Targeted therapy for patients with recurrent allergic or dry eye conditions
Emergency Eye Care Unit: 24/7 services for urgent cases such as trauma or acute infections
Imaging & Diagnostic Center: Advanced imaging including OCT, fundus photography, and orbital CT scans
What causes a red and swollen eye only on one side?
It may result from infection, allergies, trauma, or inflammation. Accurate diagnosis is key to proper treatment.
Is it dangerous to have a red eye for several days?
Yes. Prolonged redness can signal underlying issues. If symptoms last more than 48 hours, consult an eye specialist.
Can I treat eye swelling at home?
Mild swelling due to allergies may improve with cold compresses or antihistamines. Infections or trauma require medical attention.
Can children get this condition too?
Yes. Children are especially prone to eye infections like conjunctivitis, which may present with unilateral redness and discharge.
How long does it take to heal?
Recovery depends on the cause. Mild allergic reactions may clear in a few days, while bacterial infections may require a week or more with proper treatment.