Is That Sunscreen In Your Car Still Good?

tiago-macambira-hot-cars.jpgSummer is nearly here and temperatures have been heating up. That means it’s time to head to the beach. So is it OK to slather on that sunscreen that has been sitting in your trunk for a year? Probably not.

Sunscreens have a self life of about 3 years. However, most sunscreens are unstable at high temperatures (ironic, huh?). High temperatures can cause the ultraviolet absorbing chemicals like avobenzone and oxybenzone to degrade right in the bottle. When you apply a degraded sunscreen to your skin, you are not getting the SPF indicated on the bottle and in fact might be applying nothing more than a thick white moisturizer. Ideally sunscreens should be kept at temperatures no hotter than 77 °F (25°C) — the inside of your car in the beach parking lot can reach over 120° (50°C).

When you are at the beach, toss your sunscreen in the cooler; it will keep it from breaking down and will feel great on your skin when you reapply.

If you have an sunscreen that is more than 3 years old or a sunscreen that has been sitting in your car for any length of time, then buy a fresh one this summer. Otherwise, you might need this.

Post written by Jeffrey Benabio, MD. You might also like:

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Photo credit: Tiago Macambira

8 thoughts on “Is That Sunscreen In Your Car Still Good?”

  1. I often wonder how old the sunscreen is on the store shelves. Most don’t have expiration dates listed… and who knows if they were left in the sun on a shipping dock somewhere en route to the store?

    My personal experience (n=1) is that old sunblock still seems to keep me from burning. Maybe the break down of the avobenzone isn’t complete, even at high temperatures? Is skin pinkness a “good enough” test for sun block effectiveness? Can there be damage through sunblock even if burns don’t occur? I guess the answer is yes…

  2. My sunscreens use only titanium dioxide and/or zinc oxide. Could you please address the issue of whether these 1) lose effectiveness over time, and 2) break down/lose effectiveness from heat?

  3. Dr Val-
    How are you? Thanks for stopping by. You make good points. I had a patient just yesterday who related a story of buying $40 sunscreen which she dutifully applied to her and her kids faces. All three got sunburned. Something went wrong and it is certainly possible that the sunscreen itself was ineffective from prolonged shelf time or from heat.

    Your questions are excellent. I am certain that even if a sunblock like avobenzone is degraded from heat, there is still enough active product to provide protection. Remember, an SPF of 70 means you could stay in the sun 70 x longer than without sunscreen and get the same amount of UVB damage. Even if what you actually got was only SPF 20, that is still significant protection. There is damage even if you don’t burn, but the worst damage obviously is if you got enough ultraviolet exposure to cause redness and blistering.

    Pam-

    Physical sunscreens like titanium dioxide or zinc oxide are much more stable than chemical sunscreens, even the newer “stabilized” ones. They are likely more stable even at higher temperatures, but I cannot find any data to support me on that. Maybe someone else out there has it and would share.

  4. Not a good idea to keep a hold of sun screen. Most has an expiry date. In some cases it is marked on tha packaging, but you have to look closely.

  5. Lew Orban says:

    The Sun….is good for the skin and the body. The natural Vitamin D it gives us is actually a hormone that affects all our organs. So do you really think sunscreen is a good idea……? Blocking the power of the sun and its ability to break and rebuild the DNA strands of the skin cells. Certain people may have to avoid the sun…but placing on a lotion that you have no idea what is in it or where it came from…is not a smart thing to do. There is no proof that the sun causes skin cancer…if there is actual documented proof please produce the evidence. The evidence can not be here say or findings not fully understood. It has to state that the skin with no sun screen use or protection caused cancer of the skin to appear and that the sun and not the person’s diet or hats or fabrics or soaps did not cause the actual cancer. The vitamin D you are eating that is man made is missing one molecule….it is not the same thing and is made from lambs wool…also there is no regulation as to when or how much vitamin D you will get in a product..Wake Up! There is no one checking this sun screen that you are buying or anything else your putting in your mouth!

  6. Great discussion is going on this blog i’d like to join with you guys and gain knowledge from it… Thanks

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