Does sunscreen expire?

Yes. FDA rules require sunscreen to maintain its stated strength for three years, so a bottle without a printed expiration date should be treated as good for three years from purchase. Heat shortens that substantially — the bottle that spent a summer in a car is the one to throw out. Separation, a color change, a grainy texture or a changed smell all mean it is past its useful life.

The practical caveat: if a bottle lasts you three years, the real problem is that you are applying far too little of it. A household using sunscreen properly gets through it well before expiry becomes a question.

What the three-year rule actually is

The FDA requires sunscreen to retain its labeled strength for at least three years. A manufacturer may print an expiration date, in which case that date governs. If there is none printed, the three-year rule is why you can treat the purchase date plus three years as the limit.

Write the date you opened it on the bottle with a marker. It takes five seconds and removes the guesswork entirely a year later.

What actually degrades

Chemical filters

These break down over time, and faster with heat and light exposure. Avobenzone is the notable one — it is unstable in sunlight even when fresh, which is why it is almost always paired with a stabilizer. An old chemical sunscreen has genuinely less filter in it than the label claims.

Mineral filters

Zinc oxide and titanium dioxide do not chemically degrade — they are stable inorganic compounds. What fails in an old mineral sunscreen is the emulsion: the base separates, the particles clump, and you can no longer apply an even layer. Uneven coverage means uneven protection, so the outcome is the same even though the mechanism differs.

Preservatives

These degrade too, which is why an old bottle can develop a changed smell or, rarely, visible growth. That is a reason to discard regardless of the filters.

Heat is the real enemy

A car interior on a hot day reaches temperatures far above anything a sunscreen was formulated to survive, and that is where most bottles live between June and September. Heat accelerates filter degradation and breaks emulsions.

The signs to act on

• Separation. A watery layer sitting on top, or oil and solids that will not recombine when shaken.
• Color change. Yellowing in a white formula, or darkening generally.
• Grainy or gritty texture, which usually means the mineral particles have clumped.
• A changed smell — rancid, sour, or simply different from how it smelled new.
• Watery consistency in something that was previously a cream.

Any one of those means throw it out. A degraded sunscreen is not harmful so much as unreliable, and unreliable is the worst property a sunscreen can have — because you will behave as though you are protected.

Storing it properly

1. Do not leave it in a car, ever, and especially not over a season.
2. Keep it in the shade at the beach — inside a bag or under a towel, not on the sand in the sun.
3. Close it properly. Air exposure accelerates everything above.
4. Write the opening date on the bottle with a marker.
5. Buy a size you will finish, which for a household using it properly is larger than most people expect.