DEAR MAYO CLINIC: I recently took my daughter to the pediatrician because her cold caused her eyes to become red. The doctor said the redness was pinkeye. Last time my daughter had pinkeye we were given eyedrops to treat it, but this time we were told it was likely caused by a virus and eyedrops wouldn’t do any good unless her symptoms change. Why would this be?

ANSWER: Pinkeye can be caused by a virus or bacteria, though most cases are caused by a virus. Viral eye infections typically do not require any treatment. Bacterial eye infections usually are treated with antibiotic eyedrops.

Eye infections are common, especially in children. As in your daughter’s case, they often happen when a child has a cold. Viral eye infections and bacterial eye infections are called conjunctivitis, or pinkeye.

What many people think of as pinkeye most often is associated with the bacterial infection. It causes most of the symptoms people tend to think of when they hear about pinkeye: yellow discharge that causes the eyelids to stick together, and puffy eyelids. While both viral and bacterial conjunctivitis can cause eyelids to stick together in the morning, a viral eye infection does not cause continuous eye drainage throughout the day. Its main symptom is eye redness.

Viral pinkeye usually lasts as long as a cold — typically up to one to two weeks. No treatment is necessary. Because it is not caused by bacteria, antibiotic eyedrops do not help this type of eye infection. Children with viral pinkeye do not need to stay home from childcare or school. The condition is harmless and only mildly contagious.

When a child has viral pinkeye, he or she is at risk for getting bacterial pinkeye, too. Many kids end up having both types of eye infection at the same time. To help prevent that, during the time the eyes are red, gently wipe the eyelids with a cotton ball soaked in warm water about every one to two hours while the child is awake.

If you notice discharge or other matter in your daughter’s eyes that continues to appear throughout the day, contact her primary care provider to determine if bacterial pinkeye has developed. If so, her provider may recommend antibiotic eyedrops.

A typical prescription for bacterial pinkeye is one drop in each eye every four hours when the child is awake. Continue using the eyedrops until the child has woken up two mornings in a row without any pus or other matter in either eye. To prevent eye damage, contact lenses should not be worn while a person is receiving treatment for bacterial pinkeye.

Bacterial pinkeye can be spread to others if they come in contact with pus from the eyes. For that reason, people who have bacterial pinkeye should not share towels, washcloths or other personal hygiene items that may be used on the eyes or face. Washing hands often also can decrease the risk.

Unless the pus is excessive, the risk of spreading bacterial pinkeye is low after the first 24 hours of using antibiotic eyedrops. Children can return to child care or school at that time.

It is uncommon for pinkeye to lead to other medical concerns, and the condition usually goes away without any lasting eye problems. But call your daughter’s health care provider right away if you notice her eyes becoming red or swollen, if she starts to have blurry vision, if the eyes become painful, or if she develops an earache. — Stephanie Starr, M.D., Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, Minnesota

(Mayo Clinic Q & A is an educational resource and doesn’t replace regular medical care. E-mail a question to MayoClinicQ&A@mayo.edu. For more information, visit www.mayoclinic.org.)