Contact lens myths: sleeping in them, tap water, cheap online lenses, sharing: what puts an eye at risk

No. You should not sleep in contact lenses or rinse them in tap water, because both raise the risk of a corneal ulcer, an open sore on the clear front window of the eye, which can permanently damage vision. Cheap lenses from online sellers, coloured lenses worn "just for fun" and lenses shared with a friend carry the same kind of risk. A lens is a medical device that sits on the cornea, and the myths below all come from treating it as an accessory.

Is it safe to sleep in contact lenses, even for a nap?

No. A 2018 CDC report states that sleeping in lenses, whether inadvertently, occasionally or as part of a prescribed wearing schedule, increases the risk of contact lens-related eye infections six- to eightfold. The American Academy of Ophthalmology repeats the same multiplier and adds that it does not matter whether you wear extended-wear lenses, fall asleep by accident, or only do it occasionally.

The CDC report notes that about one third of lens wearers say they sleep or nap in their lenses, so this is the commonest myth and the most casual one. The reasoning people give is "my lenses are made for it", or "it was only a nap". The CDC and the Academy do not make that exception. The CDC advice is to avoid sleeping in lenses unless your eye care provider directs it, and a few lens types are designed for overnight wear on that basis. Even then, the infection risk is higher than with daily wear.

Why does it matter so much? The usual explanation is that the cornea has no blood vessels and takes its oxygen from the air through the tears, so a lens on a closed eye is a barrier to that and a place for germs to sit. That is the general account. Published guidance gives the multiplier, not the physiology.

Can I rinse or store my lenses in tap water, or wear them in the shower or pool?

No. The CDC advises keeping lenses away from all water, removing them before showering or swimming, and using fresh lens solution for storage, never water. The US FDA says not to expose lenses to any water: tap, bottled, distilled, lake or ocean water.

The reason is a microscopic organism called Acanthamoeba, found in fresh water and salt water, swimming pools, hot tubs and drinking water systems. Acanthamoeba keratitis, the infection it causes, can cause severe pain and permanent vision loss, and the CDC says it is most common among people who wear contact lenses. The CDC calls it a rare infection and says it is treatable with prescription medicines, provided you see an eye doctor right away. No Malaysian figure is given here, because none is available.

The other water rule is about the case. The Academy says to use new solution each time, never to reuse or top off old solution, and to replace the lens case at least every three months. A case full of half-used solution is a small culture dish.

Are cheap contact lenses from online sellers safe, and are they even legal in Malaysia?

They are not safe to assume, and selling them online is not allowed. On 25 March 2025 the Medical Device Authority (MDA) stated that the sale of optical devices and contact lenses on any e-commerce platform is prohibited. It cited the Medical Device Act 2012 (Act 737), section 30 of the Optical Act 1991 and the Medical Device (Advertising) Regulations 2019. These products must be registered, need a prescription, and must be prepared and dispensed by a registered optician or optometrist.

The penalty falls on the seller: a fine of up to RM200,000, up to two years in prison, or both. The Star's fact-check of the claim that contact lenses cannot be sold online in Malaysia rated it true. In March 2026, the Ministry of Health and the MDA reported an enforcement operation on 19 premises in Wangsa Maju, Kuala Lumpur, which ended in 12 warning notices for unregistered products and improper labelling. And in February 2026, the Health Minister said that online sale of cosmetic lenses cannot be handled effectively under the existing Optical Act, and that the ministry planned to table an Optometry Bill in October 2026. Whether it has been tabled is not confirmed here.

I am a surgeon, not a lawyer, so I leave the law there. For your eye the point is practical. A pair bought online has had no measurement of your cornea, no fitting and no check of what is in the packet. Little Eyes 101 covers this for teenagers in its page on coloured contact lenses bought online. For adults, the safe route is an eye examination and a prescription from a registered optician or optometrist, and the lenses dispensed there.

Are coloured or decorative lenses just cosmetic?

No. They sit on the cornea, so they are medical devices whatever the packet says. The FDA states that decorative contact lenses are medical devices and that all contact lenses, decorative ones included, must be prescribed by a doctor. It lists corneal abrasion, allergic reaction, decreased vision, infection and blindness among the risks.

The Academy's 2025 clinical statement on cosmetic lenses reports that the FDA tested more than 300 lenses and found microbial contamination in 60 per cent of the counterfeit lenses and 27 per cent of the unapproved lenses. That was an American sample, and what a Malaysian one would show is not known. It does show what a lens with no oversight can carry. The statement also describes patients who needed a corneal transplant after cosmetic lens use.

The colour does not change what a lens is. It still has to be fitted to a measured eye. Corneal abrasion, a scratch on the surface, is on the FDA's list of risks, and infection sits on the same list.

Is it okay to share contact lenses, or to wear them longer to save money?

No to sharing. The Academy says contact lenses should never be shared, and that applies to a friend's spare pair for a photo as much as to a sister's. A lens carries the germs of whoever wore it, and its shape was chosen for another cornea.

On stretching a lens past its schedule, the Academy tells wearers to follow the eye doctor's replacement schedule. It also says never to put a lens in your mouth to wet it, because saliva is not sterile.

Can years of contact lens wear affect the eyelids?

Yes, and this is the part an oculoplastic surgeon sees from the other side. Long wear is linked in the studies with a drooping upper lid, an inflamed, bumpy lid lining called giant papillary conjunctivitis, and changes in the oil glands of the lid margin. The evidence is mostly association, not proof of cause, and I set it out in my article on contact lenses and your eyelids.

Lens-related dry eye and lid problems are also why a lens that "feels fine" can still be a poor fit for the eye. If lenses have become uncomfortable by evening, or you need drops through the day, the question is the lid margin and the tear film, not another brand. Dry eye in its wider setting is in my article on dry eyes after fifty.

What should I do if my eye is red or sore while wearing lenses?

Take the lenses out, do not put them back, and have the eye examined the same day. The NHS advises an urgent appointment for a red eye in a contact lens wearer, because it could be an infection. The FDA says redness, discomfort, blurred vision or pain need prompt professional evaluation, and that you cannot judge the severity yourself.

The Academy adds that lenses should be stopped at once for significant redness, pain, watering, light sensitivity, blurred vision or discharge. Do not reach for a bottle from the pharmacy shelf first. Whitening and steroid drops are the wrong choice here, and a steroid drop can let an infection such as herpes spread, which I explain in my guide to pharmacy eye drops. If the redness comes with itching and swelling in haze, it may not be the lens at all, and the page on haze and your eyelids explains why. For how to sort one red eye from another, see my article on red eye in adults.

For the wider map of the front of the eye, see the eye surface section and my hub article on why eyes look tired.