Sunscreen: Does it have a lifespan of reliable use?
Question
I have an old bottle of sunscreen from last year. Is it still good? Or should I throw it out?
Answer
from Lawrence E. Gibson, M.D. Mayo Clinic
Sunscreens are designed to remain stable and at original strength for up to three years. This means that you can use leftover sunscreen from one summer to the next.
Some sunscreens include an expiration date — the date at which time the sunscreen is no longer effective. Discard sunscreen that is past the expiration date or is more than 3 years old.
Keep in mind, however, that if you use sunscreen frequently and liberally, a bottle of sunscreen shouldn't last you that long. A liberal application is 1 ounce (30 milliliters) — the amount in a shot glass — to cover all exposed parts of the body. If you have a 4-ounce (118-milliliter) bottle, you'll use about one-fourth of it for one application. Be sure to rub the sunscreen in well.
To maximize protection, use a broad-spectrum sunscreen with a sun protection factor (SPF) of at least 15. Apply liberally 30 minutes before going outdoors and reapply every two hours, or after swimming or sweating.