Does nail polish expire, and how to store it

A bottle of polish does not spoil the way a cream does. It contains no water, so bacteria have nothing to grow in. What it does is dry out. Every time the cap comes off, solvent escapes, and over months the formula thickens until it drags across the nail and never levels.

How long a bottle lasts is decided by how well the cap seals and where the bottle lives. The signs of a polish past its best, the storage rules that slow the clock, and the one fix that works are set out here.

How long does nail polish last in the bottle?

Unopened, Essie polish has a shelf life of 2 years, and the brand recommends replacing a polish after 24 months of use (Essie). Those figures are conservative. A polish is nitrocellulose, resins and plasticisers dissolved in volatile solvents, mainly butyl acetate and ethyl acetate (Personal Care Magazine). As long as the solvent stays in the bottle, the formula is stable, and a bottle with a tight cap in a cool drawer is often fine at 2 to 3 years.

What ends a polish is solvent loss. Essie's explanation is that product left on the neck of the bottle dries, the cap seals less and less tightly over time, and solvent exposed to the air evaporates, so the polish thickens (Essie). A bottle opened often and closed carelessly can be thick within a year. A bottle opened rarely and wiped every time can outlive the shade's fashion.

How do you know if nail polish has gone off?

Settled pigment on its own is not a fault. Shimmers, pearls and magnetic pigments are heavier than the liquid and sink in a bottle that has stood for weeks. A minute of rolling between the palms brings them back. Shaking does the same but adds bubbles, which is why Essie advises rolling the bottle upside down between the hands instead of shaking it (Essie).

What does the open-jar symbol on the bottle mean?

The period-after-opening symbol (PAO) is the small open jar printed on cosmetics packaging with a number of months inside it, such as 12M or 24M. Under the EU Cosmetics Regulation (EC) No 1223/2009, a product with a minimum durability of more than 30 months is marked with the PAO symbol showing how long it stays safe to use after opening; a product with a shorter durability is marked with a best-before date instead (EUR-Lex).

On polish the PAO is a safety statement about the formula, not a promise about how it paints. A bottle marked 24M that has been opened every week in a warm bathroom may be thick long before 24 months. A bottle marked 12M that has been kept sealed in a drawer may still paint like new after two years. Use the symbol as a ceiling and the bottle itself as the real test.

Where and how should nail polish be stored?

Cool, dark, upright, with a clean neck. Essie's guidance is to keep the neck of the bottle clean and store polish somewhere cool, out of direct sunlight; the brand adds that polish can even be refrigerated (Essie). Every one of those words does a job.

• Cool. Heat speeds evaporation and pushes solvent against the cap. Room temperature in a drawer or a cupboard is right; a windowsill, a radiator shelf or a car is wrong. The fridge is not needed, and a bottle taken from the fridge must warm up before it paints smoothly.
• Dark. Light fades some pigments and dyes. A glass bottle on a sunny shelf is a display, not storage.
• Upright. A bottle on its side keeps polish against the cap, which dries on the threads and breaks the seal. Standing, the polish stays away from the cap.
• Clean neck. Wipe the neck with a remover-dampened pad before every closing. This single habit doubles the useful life of a bottle.
• Tight cap. Close it firmly straight after the last coat, not after the top coat has been applied to all ten nails.

A bathroom is the worst room in the house for polish: warm, humid and bright. A bedroom drawer, a hallway cupboard or a closed box on a shelf are all better.

How to revive thick nail polish

Thick polish is polish that has lost solvent, so the fix is to put solvent back. Nail polish thinner is a small bottle of the same solvents the polish was made with, and a few drops restore the flow. Nail polish remover is the wrong liquid: acetone breaks down the film-former, and a polish thinned with remover goes dull, streaky and chips early.

You will need: nail polish thinner, a remover-dampened pad for the neck, and a minute of patience.

1. Wipe the neck and threads of the bottle so the cap can seal afterwards.
2. Add 2 or 3 drops of thinner to a standard bottle. More can be added later; it cannot be taken out.
3. Close the cap and roll the bottle between the palms for a minute. Do not shake.
4. Let the bottle stand for 10 minutes so any bubbles rise.
5. Test one stroke on a nail. If it still drags, add 2 more drops and repeat.
6. Stop when the polish levels in three strokes. A polish that needs more than a handful of drops in a month is losing solvent through its cap, so clean the neck more often.

Thinner cannot repair a polish that has separated into layers that will not remix, or one that has gone gritty. Those bottles go to the household chemical collection point, not the bin or the drain.

Does old nail polish become unsafe?

An old polish is a poor polish, not a dangerous one. Because the formula contains no water, it does not grow bacteria, which is why polish rarely shows the short PAO periods seen on mascara. The risks of an old bottle are practical: a thick coat that never hardens, bubbles, a dull finish and early chipping.

The exception is any product used near broken skin. A polish, thinner or remover that has been contaminated with dust, flakes or water is best discarded. A sharp change in smell is the signal to stop using a bottle, whatever its age.