Experts say colored contacts that create vampire or zombie eyes for Halloween can cause damage to the eyes. Make sure you have a prescription before using them.

Considering zombie eyes for your Halloween costume this year?

How about red vampire eyes?

You can achieve this look by using decorative or costume contact lenses.

They don’t correct your vision, but can change the color of your eye.

But experts are warning consumers to be careful this Halloween season and ensure they only purchase contacts from a reputable supplier who requires a prescription.

“It doesn’t matter if it corrects your vision or if you’re wearing it simply for fun, or in this case, to dress up in a costume for Halloween. The lens is a medical device, and in this country, medical devices are regulated by the FDA [U.S. Food and Drug Administration], meaning that the products have to be inspected and approved before they are imported into this country legally,” Dr. Thomas L. Steinemann, clinical spokesperson for the American Academy of Ophthalmology, told Healthline.

Although novelty contacts may be seen as part of a costume, in the United States they’re not considered a cosmetic. They can’t be sold over the counter without a prescription.

Beauty parlors, party shops, costume stores, and online retailers that sell contacts without requiring a prescription are breaking the law.

“If you’re buying contacts from street vendors that don’t require a prescription… that’s illegal and that’s a red flag for the buyer. If somebody is willing to sell you a lens no questions asked, they are basically involving you in an illegal trade and… it’s probably a pretty good bet that that lens is not approved for legal sale in the U.S.,” Steinemann said.

The FDA says they’re aware of multiple vendors illegally selling contact lenses in the United States for as little as $20.

They advise consumers to never buy contacts from street vendors, salons, beauty supply stores, boutiques, flea markets, novelty stores, Halloween stores, record or video stores, convenience stores, beach stores, or internet sites that don’t require a prescription.

“There is no way to know if those breaking the law and selling them without a prescription are selling quality lenses or dangerous junk. Poorly fitting or poorly manufactured lenses may cause scratches to the eye surface, which in itself are very painful,” Dr. Colin McCannel, a professor of clinical ophthalmology at the University of California, Los Angeles (UCLA) and medical director of the Stein Eye Center, told Healthline.

“Worse yet, once there is a scratch, there is an increased risk of an infection. Corneal infections from contact lenses are very serious problems, and can cause blindness,” he said.

Steinemann says some of the lenses sold illegally are made overseas using questionable products.

Those lenses that are imported into the United States without approval are in some cases contaminated with germs on the lens.

Such germs could be transferred to the wearer, who’d then be at risk of a blinding infection.

Those who wish to wear decorative lenses for Halloween can do so safely if they obtain a prescription from a qualified eye care professional.

That prescription should include a brand name, the measurements of the eye, and an expiration date.

Contact lenses aren’t a “one-size-fits-all” medical device. Both Steinemann and McCannel say it’s essential the eye is properly measured so that the lens will fit properly.

“The surface of your eye has certain measurements that your qualified eye professional — your ophthalmologist or optometrist — will measure and make sure the lens parameters fit on the surface, then look at the fit of the lens on the eye, like trying on a shoe to make sure the shoe fits,” Steinemann said.

Another benefit to obtaining a prescription for decorative lenses through a qualified eye care professional is that the wearer will then be properly trained in the appropriate way to wear and care for the lenses. This includes proper cleaning practices.

Even if decorative lenses are obtained legally, Steinemann says consumers still need to be aware of the potential risks associated with wearing costume lenses.

“One thing people may not realize is Halloween, theatrical, or decorative lenses are filled with lots of dyes. Dyes don’t allow the surface of your eye to breathe very well, so you can’t really wear a colored lens the same way somebody who is nearsighted or farsighted would wear a corrective lens that is clear. The surface of the eye requires oxygen from the atmosphere, so when you have a piece of plastic — or worse yet a piece of painted plastic — that is impeding oxygen flow, that’s not very healthy for the eye,” he said.

Symptoms such as redness or pain in the eye, feeling as if something is in the eye, light sensitivity, or a decrease in vision are all signs of a possible eye infection. They require immediate attention from a qualified eye care professional.

Steinemann advises people to think carefully about whether they need costume contacts this Halloween, and to not take any risks by buying from a vendor that isn’t an authorized distributor of contact lenses.

“It’s not worth it. For one night of fun, it’s not worth going blind,” he said.