Does sunscreen expire?
Both chemical and physical sunscreens (those containing zinc oxide or titanium dioxide) can deteriorate over time. Sunscreens are designed to remain stable and at original strength for up to three years, so check the bottle or tube for the expiration date.
Some sunscreens include an expiration date, or an indication of when the sunscreen is no longer effective. However, most sunscreens do not have expiration dates printed on them. If there is no expiration date, you can always call the customer service number listed on the label. You can provide them with the codes that are printed on the bottle and they can tell you if it has expired. The codes printed on the label track the date, batch, and location of where your bottle was manufactured. For optimal sun protection as well as texture, stability, and sterility, use the sunscreen prior to the date listed.
Discard sunscreen that's past the expiration date, is more than three years old or has been exposed to high temperatures.
If you can't find a date, or if the product seems to have dried up or changed color or consistency, it's better to be safe and buy some new sunscreen.
Sunscreens are tested in their actual containers, since plastics in the container may leach into the sunscreen and cause a chemical interaction. UVR changes the molecular structure of chemical sunscreens, so sunscreen containers should be opaque.
For best results, use your sunscreen before the stated expiration date, and store it in a dry, cool place with the lid tightly fastened.
Keep in mind, however, that if you use sunscreen generously and frequently, a bottle of sunscreen shouldn't last from one year to the next. Generally, a liberal application is 1 ounce (30 milliliters) — the amount in a shot glass — to cover all exposed parts of the body.
The American Academy of Dermatology recommends using a broad-spectrum sunscreen with an SPF of 30 or more. Apply sunscreen generously 20 to 30 minutes before going outdoors and reapply about every two hours — or more often if you're swimming or sweating. Make sure to rub the sunscreen in well.
Now you know the answer to the question, "When does sunscreen expire?" But when you are in doubt just toss the old sunscreen and buy a new one.