You're basically bathing your eyes in nasty germs.

We all have some personal habits that aren't so hygienic. (Talking to you, people who bring their phone into the bathroom stall.) But there’s a fine line between a gross habit and a serious health risk.

Licking your contacts to moisten them before putting them back in your eyes comes under the latter category. People do it, especially when they're away from home without any solution nearby to use instead. But seriously, stop. You're basically giving your eye the equivalent of a germ bath and putting your sight at risk.

“Your mouth is probably one of the dirtiest locations in your body,” says Thomas Steinemann, MD, an ophthalmologist in Cleveland and clinical spokesperson for the American Academy of Ophthalmology. “It’s filled with bacteria.”

Most people wear soft contact lenses, which will absorb whatever liquid they come in contact with. So if you lick your contacts, they’ll soak up all of the bacteria in your saliva. When you put your contacts back in your eyes, those germs will go straight into your cornea and will set you up for an infection.

A corneal ulcer (also called keratitis) is an infection of the outermost layer of the eye. “If you don’t treat it aggressively, you can suffer vision loss or even blindness from it,” Dr. Steinemann warns. Keratitis can be extremely painful and may be caused by bacteria, a fungus, a virus, or a microbe called Acanthamoeba (a single-cell living organism) entering the cornea.

Early symptoms of keratitis can be minor; your eye might feel scratchy, irritated, or light-sensitive. But Dr. Steinemann says it will very quickly escalate and become severely painful—necessitating a trip to the ER and antibiotics.

If you lick your contacts and develop mild symptoms that don't get worse, however, you could have pink eye, aka conjunctivitis, Dr. Steinemann says. Pink eye isn't a serious threat to your vision, but it is pretty gunky and disgusting. It can be caused by bacteria or a virus, and if it's the former, your MD can cure it with antibiotics.

So what do you do if your contact falls out with solution nowhere in sight? If you don't have your glasses on you to wear until you get home, head to the nearest drug store and buy some solution. No exceptions.

Don't try to wet them by running them under the faucet or a water fountain. “With tap water, even though it’s pure to drink, it’s not sterile, and it has things that could potentially harm your eyes,” Dr. Steinemann says. The same goes for water from the lake, pond, ocean, or pool.

Another common mistake is thinking that saline actually cleans your contacts. Saline is just a wetting agent. So if your contact falls out and gets dirty, you need to clean it with a disinfectant, such as a multi-purpose disinfecting solution.

If you’re having problems with dry or irritated contacts that fall out or force you to remove them, it’s time to consult your eye doctor. “Try to figure out why it is that the contacts are giving you so much trouble,” Dr. Steinemann says. “Don’t just say ‘Oh, I guess my eyes are dry’ or ‘I guess it’s seasonal allergy.’”

Your ophthalmologist can get to the bottom of the problem and put an end to that gross licking habit.