Yes, pink eye is common. But can it be prevented?

While many conditions and diseases such as high blood pressure, early-stage cancer, and diabetes are not visually apparent in most people and can preserver for years before being discovered, other conditions are easy to spot and often laden with obvious symptoms.

Someone with acne, for instance, clearly has a skin condition; just like someone wearing eyeglasses probably has an eye disorder. An individual throwing up is plainly sick, and someone who snores extensively and stops breathing for periods of time as they do almost certainly has sleep apnea.

But one of the most obvious conditions is also the most common. Pink eye has telltale symptoms most everyone recognizes and affects some six million people annually in the United States.

What is pink eye?

Pink eye is what occurs when the thin membrane that lines the white of the eye and the eyelid becomes infected and inflamed. The condition is also called conjunctivitis because the name of the affected membrane is the conjunctiva.

When pink eye occurs, there's "usually a discharge of the conjunctiva that can be thin (like tears), thicker like mucus, or can be like pus," says Dr. John Epling, a practicing family physician and a professor of population health at Virginia Tech Carilion School of Medicine. This discharge can be clear, yellow, or green, and is usually sticky in nature - sometimes causing the individual to wake up with their eyelids stuck together.

Other common symptoms of conjunctivitis include watery eyes, "redness of one or both eyes, itching, and mild discomfort," says Dr. Daniel Shapiro, a pediatric emergency care physician at UCSF Benioff Children’s Hospital in San Francisco.

The virus or bacteria that causes many cases of pink eye can spread easily from person to person or object to person, so individuals with conjunctivitis are discouraged from touching others or sharing towels, pillows, blankets, or makeup until they are no longer contagious - a period that usually lasts "a few days to a week," notes Epling.

What causes pink eye?

Pink eye appears the way it does because, when the small blood vessels in the conjunctiva become swollen and irritated, it makes them appear more visible, notes Mayo Clinic.

This swelling and irritation can be caused by a number of things, but viruses and bacteria are the most common. Bacteria entering the eye such as Staphylococcus aureus and Streptococcus pneumoniae can cause pink eye. Sleeping on a pillow where bacteria is present or wearing contact lenses that are dirty or aren't your own are common ways bacterial conjunctivitis can develop.

Most viral cases of conjunctivitis are causes by the adenovirus; but other viruses such as the measles (rubeola) virus, the Epstein-Barr virus, the vaicella-zoster virus (which also causes shingles and chickenpox), and the herpes simplex virus can also cause pink eye.

Shapiros says that chemical irritation can also lead to pink eye; as can coming into direct contact with toxins - though he says such cases are uncommon.

The National Eye Institute also notes that allergens such as pollen, dust mites, mold, and dander can also cause or contribute to pink eye. In babies, red eye is called neonatal conjunctivitis and is often caused by a blocked tear duct.

How is pink eye treated?

While most cases of pink eye resolve on their own and are not worrisome or dangerous, "conjunctivitis does not typically involve changes in vision, sensitivity to light, or severe pain," Shapiro cautions, "so when patients with red eyes have these symptoms, alternative diagnoses should be considered and referral to an ophthalmologist may be warranted."

Unless the condition has such symptoms or appears to be worsening though, mild symptoms can be managed at home without needing medical treatment. Such symptoms can be helped by gentling cleaning the outside of your eye with warm water to remove crust and avoiding aggravating your symptoms by scratching or rubbing your eyes.

For moderate to severe infectious conjunctivitis or pink eye caused by bacteria, topical treatments "may reduce the duration of symptoms," says Shapiro. These may include topical antibiotics, artificial tears, or lubricating eye drops. "Oral antibiotics are not typically warranted for conjunctivitis but may be prescribed in special circumstances or if there are rare complications," he says. "For allergic conjunctivitis, the most effective treatment is avoidance of the offending exposure."

This article originally appeared on USA TODAY: What is pink eye?