There will be plenty of ghosts and goblins making the rounds this Halloween and for some, it’s tempting to take things to the next frightening level. But there’s one particular add-on you should avoid for health reasons, officials warn.

Officials with the Centers for Disease Control and Prevention are warning against decorative contact lenses that are sold to change the wearer’s appearance. The lenses – sometimes called fashion, costume, or colored contact lenses  – are often sold at costume shops, beauty salons, beauty supply stores, drug stores or online and don’t require a prescription.

The lenses aren’t designed to improve your vision – just to change the way your eyes look.

“When decorative contact lenses are sold without a prescription, proper fitting, and education from an eye doctor, there may be a higher chance of contact lens-related eye problems,” the CDC said.

The problems can include scratches to the outer layer of the eye or ulcers on the cornea, the clear covering over the front of the eye. The result from either can be scarring, infection, and permanent vision reduction or loss. The lenses, which aren’t measured to ensure they fit the eyes correctly, can also cause conjunctivitis, decreased vision or even blindness.

Also, the over-the-counter lenses often don’t come with instructions on how to clean and care for them. Failure to use a proper solution to keep the lenses clean and moist can lead to infections, some of which can spread rapidly, some in as little as 24 hours if not diagnosed or treated properly.

The best idea, according to the CDC, is to avoid the lenses. If you did use the lenses and experience redness, eye pain that doesn’t go away after a short time or a decrease in vision, you should see an eye doctor immediately.