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When your eyes become bloodshot due to allergies or other causes, your first impulse may be to try whitening eye drops to soothe the irritation and restore the brightness of your eyes.

Whitening eye drops are also known as redness-relieving eye drops. Several types are available, each differing in their chemical makeup, and thus the way they work.

Whatever whitening eye drops you choose, read the instructions carefully. Using too much may actually make your red eyes redder or cause other unwanted side effects in the long run.

Read on to find out how whitening eye drops work, tips for keeping your eyes bright and healthy, and more.

Whitening eye drops mainly work in one of these two ways to make your eyes whiter:

  • Narrowing blood vessels. Some redness-relieving drops include medications that cause the blood vessels in the eyes to narrow (constrict). This makes the blood vessels less visible, reducing the red hue in the sclera (white part of the eyes).
  • Adding moisture. Other eye drops contain lubricants to prevent dryness and moisturize the whites of your eyes to make them feel better, and in some cases look whiter in the process.

Keep in mind that some causes of red eyes may need more than whitening eye drops to clear things up. A bacterial infection, for example, may require antibiotic eye drops prescribed by a doctor.

But for treating routine causes of red eyes, the following ingredients for eye drops may be helpful.

Decongestants

Most of the widely used eye drops — both prescription and over-the-counter (OTC) varieties — contain decongestants or antihistamines.

Decongestant eye drops work by narrowing the blood vessels in the eyes. When blood vessels widen, they can sometimes be visible, making the eyes look bloodshot. Other times, they give the sclera a red or pinkish hue.

Decongestant eye drops include tetrahydrozoline (Visine) and phenylephrine ophthalmic (Prefrin).

Antihistamines

Antihistamines block the action of a chemical called histamine, which is released by cells in response to an injury or allergic reaction. Histamine, which triggers an inflammatory reaction in the body, can cause many symptoms, including itchiness, sneezing, and red eyes.

Examples of antihistamine eye drops include ketotifen (Zaditor) and azelastine (Optivar).

Some eye drops contain both a decongestant and antihistamine, such as the combination naphazoline/pheniramine (Naphcon-A).

Briminodine

Originally FDA-approved as a drug to treat glaucoma, brimonidine ophthalmic (Lumify) also helps reduce swelling of blood vessels in the eyes. It’s in a class of drugs called alpha-adrenergic agonists, and it works by reducing fluid levels in the eye.

Lubricants

Also known as artificial tears, lubricating eye drops are most helpful when your eyes are dry and irritated, such as from exposure to a dry or windy climate or looking at a computer screen for a prolonged period.

Active ingredients in lubricating eye drops are somewhat similar to those in actual tears.

The OTC product Refresh contains carboxymethyl cellulose, a compound that has the ability to remain on the eye for a longer period than more watery eye drops.

OTC and prescription eye drops are generally safe to use, though you want to make sure any product you put in your eye has been approved by the Food and Drug Administration (FDA).

If you try eye drops and your eyes feel irritated or uncomfortable, tell your doctor. You may need to try another brand or cut back on how often you use the product.

Many labels for eye drops suggest placing one to two drops in each eye, up to four times a day. According to the American Academy of Ophthalmology, if you need to apply eye drops that frequently over a few days to treat redness, you should have your eyes examined by an ophthalmologist. This eye care specialist can determine what’s causing your symptoms.

The effects of eye drops that cause blood vessels to narrow can wear off, and the eyes can become redder than they were before drops were used.

This side effect is called rebound redness, and it can worsen over time. So you may want to consider using lubricating eye drops first to see if they’re sufficient for making your eyes look and feel better.

Some eye drops also contain preservatives to give them longer shelf life. But preservatives can irritate the eye. Look for preservative-free eye drops instead.

In general, redness-relieving eye drops shouldn’t be used for more than 72 hours. If redness or other symptoms linger after 3 days, you should see an eye doctor (ophthalmologist or optometrist) for an evaluation.

If you have narrow-angle glaucoma, you shouldn’t use redness-relieving eye drops made from decongestants. They can worsen your condition and cause the development of angle-closure glaucoma, which is a medical emergency.

Glaucoma is treated with a variety of medications, including prescription eye drops that help reduce pressure inside the eye.

A word on tinted eye drops

Popularized by celebrities and a lot of media coverage in 2016, blue-hued eye drops are supposed to temporarily counteract any yellow or red in the sclera to make eyes seem whiter and brighter.

A French product called Collyre Bleu Eye Drops, for example, contains ingredients such as boric acid and a blue dye called C1420651. The FDA found this blue dye ingredient, also known as methylene blue, unsafe and potentially toxic. Sale of these eye drops in the United States has since been banned.

You can take other steps besides using eye drops to help avoid redness and eye irritation. Here are a few tips to try:

  • Stay hydrated and avoid dry air. Like every part of your body, your eyes rely on healthy fluid levels to work and feel their best. But exposure to indoor or outdoor environments that are too dry can easily rob your eyes of some of their moisture.
  • Take 20-second eye breaks every 20 minutes if you work at a computer or are watching television. Allow your eyes to rest to avoid eye strain, which can lead to redness, dry eye, and eye fatigue.
  • Make sure your diet includes sources of key vitamins, including vitamins A, C, E, and B complex. Nutrients such as lutein, zeaxanthin, and omega-3 fatty acids also support eye health.
  • Get at least 7 to 8 hours of sleep per night to allow your eyes to rest.
  • Wear sunglasses with ultraviolet (UV) ray protection.

Whitening eye drops can provide some fast-acting results, reducing redness caused by allergies or certain other triggers.

If the cause of eye redness is something like conjunctivitis (pink eye), you need medicated eye drops to treat the problem.

When eye redness is likely caused by dry air or allergies, give lubricating eye drops a try first, and then consider drops with medication.

And if you find you’re also having pain or any other eye symptoms, see an eye care professional soon.