According to the American Academy of Ophthalmology (AAO), a bright white sclera (the white part of the eye) is a sign of health. Any discoloration can indicate various health issues.

Allergies are a common culprit. Exposure to pollen, dust, or chlorine from swimming pools can irritate the eyes. In response, the eyes produce histamine, which increases blood flow in the small surface blood vessels, causing redness.

Dry eyes occur when the eyes don't produce enough tears or the tear film, the protective layer of moisture covering the eyes, is unstable. This makes the eyes prone to redness and irritation, especially in dry climates, when exposed to smoke, or with prolonged contact lens wear.

Lack of sleep can hinder the eyes' necessary restorative processes. This can cause blood vessels to dilate, leading to red eyes. Insufficient sleep deprives the eyes of oxygen, making blood vessels more likely to overload and resulting in redness or red spots.

Conjunctivitis, also known as pinkeye, occurs when the conjunctiva, the membrane lining the eyelids and covering the white part of the eye, becomes irritated or infected. Bacterial and viral conjunctivitis are contagious and often accompanied by a burning sensation and watery eyes. Treatment varies depending on the type of conjunctivitis and may include antibiotics.

Unlike general eye redness, a subconjunctival hemorrhage appears as a bright red spot on the white of the eye. This happens when blood vessels in the eye rupture, often due to eye trauma, sneezing, or coughing.

Other conditions, such as corneal ulcers, can also cause red eyes. A corneal ulcer is an open sore on the cornea, often caused by infection or dry eyes.

According to the AAO, more serious eye conditions like glaucoma, blepharitis, scleritis, ocular lymphoma, herpes zoster (shingles), and uveitis can also cause red eyes.

Several treatments are available for red eyes. Artificial tears can reduce irritation and wash away allergens. Antihistamine eye drops can relieve itching caused by allergies. Applying a cool washcloth to the eyes several times a day can also help. Avoiding smoke, fumes, pollen, dust, chlorine, pet dander, and touching the eyes can also reduce redness.

Bao Bao (According to Prevention)