We’ve all done it. We purchase multiple tubes or twin-pack sunscreen sprays since they are on sale only to have used barely one of them during summer vacation. Then we store them in our cupboard or trunk until next season when we frantically look for them during an unexpected sunny outing. This goes on season after season until someone decides to check a sunblock’s expiration date, only to find it 3 years old. So what happens if your sunscreen has expired?
The FDA recommends discarding sunscreen if it is past its expiration date. If your sunscreen doesn’t have an expiration date, the FDA suggests discarding it 3 years after purchase.
Moreover if the color changes or it has an odor, the product should be discarded as well.
Expired sunscreens, or those stored in the heat or improperly, can lose its effectiveness. The chemicals within are not always stable for long periods of time and can degrade. Sunscreen/block stored in a hot car or in a moist or very dry environment can also cause unpredictable changes to the chemicals within……and trust is a huge issue when it comes relying on one’s sunblock to protect against the strong sun’s rays.
Here’s the scoop on sunscreen:
What is the difference between sunscreens and sunblocks?
Sunscreens are products that absorb the UV rays, sunblocks disperse them, providing sort of a shield.
How do they work?
Sunscreens/blocks use chemicals to disperse or absorb UV rays. Inorganic compounds in sunblocks such a titanium dioxide or zinc oxide attempt to scatter the UV rays. Organic compounds in sunscreens such as PABA and oxybenzone attempt to absorb UV rays so they can’t damage the skin.
What’s the difference between UVA and UVB radiation?
UVA rays penetrate deeply into both the epidermis and dermis. They can cause premature aging of the skin, wrinkles, and skin cancer.
UVB rays are shorter and primarily affect the epidermis. They are responsible for causing sunburns as well as skin cancer.
What is SPF?
SPF stands for Sun Protection Factor. The higher the SPF, the less sun photons enter the skin and cause damage. SPF primarily measures the protection against UVB rays. We multiply the SPF factor by how long it takes one’s skin to burn by the SPF number to determine the protection factor.
In theory, an SPF of 30 suggests your skin, if it burns within 10 minutes without protection, will not burn until 300 minutes has lapsed (30 times 10). However, we find this isn’t always the case. People sweat or swim and the sunscreen dissipates. Moreover many don’t put on the proper amounts (see below.)
So instead we use SPF as a grade to how much protection the product can offer.
- An SPF of 15 blocks 93% of UVB rays
- An SPF of 30 blocks 97% of UVB rays
- An SPF of 50 blocks 98% of UVB rays
As we see, the relationship is not linear, however the higher the SPF, the more protection we have against UV rays..
IMAGE FROM BADGERBALM
Although the SPF alludes to protection against burning, hence UVB rays, a sunscreen may still protect against both UVA rays and UVB rays if it’s a broad spectrum sunscreen.
How to apply sunscreen
Most people apply sunscreen incorrectly or unevenly. Lotion needs to be applied at an amount of 2mg/cm2 of skin or 1 teaspoon per body part (chest, arm, leg, face and neck). It should be applied 15 minutes prior to going out into the sun and needs to be reapplied every 2 hours, or more often if swimming or sweating.