Sunglasses and salt water: what it does and how to stop it

Salt water does its damage as it dries. While the glasses are wet, almost nothing is happening. As the water evaporates, salt crystallises on every surface it was dissolved in — the lens, the groove, the hinge barrel, the screw threads — and from that point it is working against you.

Which means the fix is simple and time-sensitive: rinse in fresh water before it dries.

The three separate problems

Worth separating, because they need different things and only one is obvious.

Abrasion. Dried salt crystals are hard and angular. A lens with dried salt on it has sandpaper on it, and the next wipe — with a cloth, a shirt, a towel — drags those crystals across the coating. The fine scratching that results is permanent and is the single commonest way sea-used sunglasses are ruined.

Coating degradation. Salt water is mildly corrosive and lens coatings are thin films. Repeated wet-dry cycling degrades anti-reflective and mirror coatings, which shows as clouding, patchiness or a rainbow sheen that cannot be cleaned off. Mirrored lenses suffer most.

Hardware corrosion. Hinge screws are usually steel. Salt plus water plus oxygen corrodes steel, and a corroded screw seizes in its thread. A seized screw cannot be removed, which means the hinge cannot be serviced and a future repair is impossible. Spring hinges, with an internal piston, are worse — they have more steel and more places for salt to sit.

And a fourth, mechanical: salt crystals in the lens groove hold the lens at the wrong depth and work it loose. This is one of the causes in when a sunglasses lens pops out.

The routine

Thirty seconds, same day, and it prevents all of the above.

Rinse under running fresh water, lukewarm. Both lens faces, the frame, the nose pads, the arms.

Work the hinges under the water — open and close each arm five or six times while the water runs over them. This is the step people skip and it is the one that saves the screws. The motion carries fresh water into the barrel and flushes dissolved salt out.

Rinse the nose pads specifically, where salt and suncream collect. Sunglasses nose pads covers replacing hardened ones.

Then dry with a microfibre cloth, gently. Dry rather than leaving them to air dry, because air drying leaves whatever salt is still in the water behind as crystals.

If you cannot rinse immediately, rinse later — it is still worth doing, because dissolving the salt is the goal and water does that whenever it arrives. Just do not wipe them in the meantime.

If there is sand as well, rinse before any contact with a cloth. Sand is mineral and harder than salt. Best sunglasses for the beach covers keeping it out.

What never to do

Never dry-wipe a salty lens. The most important line here. Rinse first, always.

Never use hot water. Heat softens frames and risks delaminating a polarized or mirrored lens, which is a laminate. Lukewarm is the limit, and the heat failure mode is covered in sunglasses left in a hot car.

Never leave them to dry in the sun on a hot surface, which combines the heat problem with the crystallisation problem.

No household cleaners. Window cleaner, degreasers and alcohol-based sprays attack coatings. Mild dish soap diluted in water is the strongest thing that belongs near a lens.

No paper towel or tissue. Wood fibre is abrasive on a coating.

No shirt hem. It has dust in it, and it is the way most lenses acquire their first scratches.

When it is already too late

Some damage cannot be undone, and it is worth knowing which so you do not waste money trying.

Fine scratching on the coating: permanent. No polish or treatment restores a coated lens. Products sold for this generally remove more coating.

Clouded or patchy coating: permanent. The film is degraded. Replacement lenses are the only fix, and the economics are in sunglasses lens replacement.

A delaminated polarized lens — visible as a bubble, a haze or a patch where the polarization has stopped working: permanent.

A corroded screw that still turns: replace it now, before it seizes. Screws are cheap and available in kits.

A seized screw: an optician can sometimes drill it out. Often it is the end of the frame as a serviceable item.

A squeaking or grinding hinge: usually recoverable with a proper clean. Squeaking sunglasses hinges covers the method — clean first, lubricate barely, never WD-40.

Prevention at the beach and on a boat

A retainer cord, so they do not go in the water in the first place. On a boat this is not optional. Sunglasses straps and retainers covers types that handle wet conditions.

A hard case, kept out of the sun.

Fresh water in a bottle on a boat or a long beach day, which lets you rinse before the salt dries.

Do not swim in them. Goggles are the right tool and cost very little — sunglasses for swimming.

A cheaper pair for sea use, which is a legitimate strategy rather than a compromise. Salt is hard on eyewear and an expensive frame in a boat is a decision.

Rinse the case too if it has been wet, because salt in a case transfers to the lens.

Chlorine, for comparison

Similar outcome, different mechanism.

Chlorinated water degrades coatings chemically rather than mechanically, and the result is the same permanent clouding. It is at least as hard on mirror and anti-reflective finishes as salt.

It does not crystallise, so the abrasion problem is smaller.

It still corrodes hardware.

Same fix: fresh water rinse, same day. Poolside wear counts — spray reaches the lenses even if you never get in.

Sweat is the quiet version

Worth adding, because people who never go near the sea get the same hinge failures.

Sweat is salty, and it goes into the hinges every time you wear sunglasses while running, cycling or working outdoors. It crystallises the same way and corrodes the same screws.

Which means the rinse routine is not just for the beach. After a hot or sweaty day, the same thirty seconds applies — and it is the difference between hinges that last years and hinges that squeak by the second summer.

The case, the cloth and the bag

Three things people clean the glasses and then put them straight back into.

The case. If the glasses went in wet and salty, the lining absorbed salt water and is now holding dried salt against the lens every time they are stored. Rinse a fabric-lined case and dry it thoroughly, or it undoes the whole routine.

The microfibre cloth. A cloth used to dry salty lenses all week is loaded with crystals and has become an abrasive pad. Rinse cloths in fresh water and let them dry, and carry a second.

The beach bag. Sand and salt accumulate in the bottom of it across a holiday, and a pair dropped in loose collects both. The hard case solves this.

Spotting corrosion before it seizes

Worth a look every few weeks if you use sunglasses near the sea.

Check the screw heads. Rust-coloured staining around the head, or a slot that looks rough rather than clean, means corrosion has started.

Try the screw. If it turns, replace it now — screws cost pennies and a seized one can end the frame.

Check for white crusting in the hinge gaps, which is salt that has never been flushed. Clean it as in the routine above rather than lubricating over it.

Frequently asked questions

The short version

Rinse in fresh water the same day, hinges worked under the tap, then dry with a microfibre cloth. That is the whole routine and it prevents everything in this piece.

Never dry-wipe a salty lens. Dried salt is abrasive, and the scratching it causes is permanent.

Coating damage and seized screws cannot be undone, so prevention is the only approach.

And remember that sweat is salt water too — the same rinse applies after any hot day, not just after the sea.