TL;DR
The single most important rule for a contact lens case is that tap water never touches it. Rub and rinse the case with fresh contact lens disinfecting solution, tip out the solution, and let it air dry face down on a clean tissue. Eye care guidance is to replace the case at least every three months, and many people replace it with every new bottle of solution.
Why tap water is the line you do not cross
Tap water in the United States is safe to drink. It is not sterile, and the difference matters enormously to an eye.
Water systems can carry Acanthamoeba, a microscopic organism that lives in tap water, well water, hot tubs, pools, and lakes. It is harmless when swallowed and dangerous when it reaches the cornea. Acanthamoeba keratitis is rare, extremely painful, and can permanently damage sight.
A lens case rinsed with tap water and then filled with solution can carry that organism straight to the lens and then to the eye. Contact lens solution is a disinfectant, not a guarantee, and some solutions handle Acanthamoeba poorly.
So the rule is absolute. No tap water in the case, on the case, or on the lenses. No showering or swimming in lenses either, unless your eye doctor has told you otherwise.
Source: U.S. Centers for Disease Control and Prevention guidance on contact lens hygiene
How do you clean a contact lens case?
Empty the old solution, rub the inside of each well with fresh disinfecting solution and a clean fingertip, rinse with more fresh solution, and tip the case upside down on a clean tissue to air dry with the caps off. Never rinse it with tap water and never top off old solution.
The daily routine
1. Put the lenses in first, then deal with the case. Cleaning the case while the lenses are still in it is not possible, and doing it at night leaves the case damp all day.
2. Tip out every drop of old solution. Do not save it. Do not add fresh solution to old solution, a habit sometimes called topping off. Old solution has already been used up disinfecting whatever came off the lenses.
3. Rub each well with fresh solution. A few seconds of physical rubbing with a clean fingertip removes the film that a rinse leaves behind. Rubbing is what does the work.
4. Rinse with fresh solution. Not water. Not saline unless your eye doctor says so.
5. Air dry face down, caps off. Set the case upside down on a clean tissue. Drying is a disinfection step in itself, because most of the organisms that matter do not survive a fully dry surface.
6. Never wipe it dry with a towel. Towels shed lint and carry bacteria.
Wash and dry your hands before any of this. Hand hygiene matters more here than the case cleaning does.
What that film inside the case is
Left alone, a lens case develops a slick layer on the inside walls. That is biofilm -- bacteria and sometimes fungi bound to the surface in a protective matrix.
Biofilm resists disinfecting solution. Once it is established, filling the case with fresh solution does not clear it, which is why rubbing and drying matter and why cases get replaced rather than rescued.
A cloudy or white haze is different: that is usually dried solution residue or mineral deposit. It still means the case is not being emptied and dried properly.
The same physics governs the containers everything else on a bathroom counter sits in, which is why our guide to cleaning the personal items you use every day keeps coming back to drying.
How often should you replace a contact lens case?
At least every three months, according to standard eye care guidance, and immediately if it is cracked, will not seal, or has visible film that does not rub off. Many people find it simpler to open a new case with every new bottle of solution, since the two run out at roughly the same rate.
Things that quietly go wrong
Storing the case in the bathroom. Toilets and sinks aerosolize droplets, and a damp bathroom slows drying. A bedroom drawer or a shelf away from the basin is better.
Leaving the caps on to dry. Capped wells stay damp. Off, upside down, open air.
Reusing a travel case for months. Travel cases are cases. Same three-month rule.
Buying decorative cases. Some are not made to the same standard as the ones packaged with solution. The plain ones that come free with a bottle are usually the safer choice.
Cleaning the case with soap. Soap residue irritates eyes. Fresh solution only.
Any exposure to water. Including a splash while brushing teeth, which is another argument for keeping it out of the bathroom. The same principle appears in how to clean a denture case, where drying is the whole game.
When to call an eye doctor rather than clean harder
Redness, pain, blurred vision, light sensitivity, or a feeling that something is in your eye are not cleaning problems. Take the lenses out and call an eye care professional the same day.
An eye infection can move quickly, and delaying while trying home fixes is how mild problems become serious. Bring the case and the lenses with you if you can, because they can be tested.
Nothing in a cleaning routine treats an eye condition. Good case hygiene reduces one source of risk. Your eye doctor sets the rest of the plan, including how long you may wear your specific lenses and which solution suits your eyes.
Glasses have their own set of do-not-do rules, especially around coatings, and those are covered in how to clean eyeglass lenses without scratching. For the general problem of things that stay wet in a bathroom, see how to clean a slimy toothbrush holder.
FAQ
Can you rinse a contact lens case with water?
No. Tap water is not sterile and can carry Acanthamoeba, an organism that causes a rare but sight-threatening corneal infection. Rinse the case only with fresh contact lens disinfecting solution, and keep water away from your lenses, your case, and your hands while handling lenses.
How often should a contact lens case be replaced?
At least every three months under standard eye care guidance, and right away if it cracks, will not close, or keeps a film after rubbing. Replacing the case with each new bottle of solution is an easy way to stay on schedule without tracking dates.
Why does my contact lens case get slimy?
That slime is biofilm, a layer of bacteria bound to the plastic. It forms when the case is not rubbed clean, not emptied fully, or not allowed to dry. Once biofilm sets in, fresh solution will not clear it. Rub, rinse with solution, air dry face down, and replace the case on schedule.
Should you dry a contact lens case with a towel?
No. Towels shed lint and carry bacteria from hands and skin. Tip the case upside down on a clean tissue with the caps off and let it air dry. Drying is itself a disinfection step, because most organisms that cause trouble do not survive a completely dry surface.
Is it okay to top off old contact solution?
No. Topping off means adding fresh solution to used solution, and used solution has already spent its disinfecting power. It is one of the most common contact lens hygiene mistakes. Empty the case completely every morning and use fresh solution every night.
Where should you store a contact lens case?
Somewhere dry and away from the sink and toilet, such as a bedroom drawer or a cabinet shelf. Bathrooms are humid, which slows drying, and splashes from a basin can put tap water into a case. Store it open and upside down until you need it.
Keeping the surfaces around a bathroom or bedroom clean makes small hygiene habits easier to keep. If you would rather hand that part off, get a quote or read more about house cleaning services.