Does sunscreen lose its effectiveness over time? If yes, how long does it take?

Question

I'm talking about the sunscreen that I bought for last summer ... I don't want to end up burned up testing it, so I'm wondering if there is any reason to suspect that it is now ineffective. I bought two thinking I'd use them up but I didn't and I basically have two full bottles left. They are the exact same product. If it helps, the active ingredients listed on the bottles are Octinoxate and Oxybenzone. If these are tough chemicals, do creams go bad?

There are no expiration dates on the bottles.

Also, I don't know if I'll even use them this summer, so I was wondering, well, you read the first question ...

Answer 1

On the one hand I would say go ahead and use them, if they do not seem to protect enough, get some new.However, I did sunscreen testing in my chem lab with students and the left over bottles that were donated by other teachers did seem to lose UV protection over several years. If they are only 1 year old they should be fine. We were using the ends of bottles that ay have been 5 years old.

Answer 2

It depends on the mechanism for blocking.

Physical blockers like Zinc Oxide (the white stuff) don’t realty degrade.

The chemical blockers (the stuff that eventually does not show on your skin after it is wiped in) do degrade. These sunscreens have fragile compounds in them that are broken down when UV light hits them. This way it is the compound that is harmed by the sun’s light rather than your skin. Of course this means that eventually the sun will break down your sun screen and pass right through. That is one of the reasons you do have to re apply it sometimes.

Over time in the bottle your sun screen can break down too. The compounds are fragile. Other things can cause damage to them: Oxygen, pH change (which happens from CO2 absorption from the air), and other sources of light. So your sunscreen is a perishable item, you might as well use it up.

Answer 3

Examples of strong sun block chemicals would be TiO2 and ZnO. They do not easily decompose or degrade.

So its not the sun protective chemical that lose potency. It is the cream, oil, etc. that you apply to your body that wears off. If you go into the water it may wash off. If you sweat, this will have a similar effect.

Answer 4

depending on the spf (sun protection factor) of your sunscreen. If you have 45 it means you are 45 times your skin's natural protection. The smaller the spf the more you have to reapply. 45 will last up to eight hours unless you go swimming and towel dry.

Answer 5

in case you want to keep your babies secure from the sunlight I advise preserving clothing (hats, lengthy sleeves ...). stay faraway from the chemical filters and avert aswell the nano-sized metal oxide filters. before you take advantage of sunscreen you need to know that that's a topic of fierce debate correct this second no matter if sunscreen prevents epidermis cancer or it will enhance the incidences of epidermis cancer (highly malignant cancer). regrettably the critiques of the sunscreen skeptics are a concepts underrepresented contained in the oftentimes happening press - probable through economic interests of the beauty marketplace. before each and everything: cancer and sunburn are brought about via completely diverse mechanisms. Sunburn is brought about via the direct DNA harm that's presented on via UVB. compared the malignant cancer - which causes maximum fatalities - is almost solely brought about via the oblique DNA harm that stems from loose radicals. Many sunscreens forestall the direct DNA harm yet they enhance the quantity of loose radicals. Sunscreen is meant to stay on the floor so as that it does no longer get in contact with residing tissue. regrettably a small fraction of the chemical aspects continuously penetrates via the epidermal barrier with time. even as sunscreen molecules are in contact with residing tissue and then they are excited they become very reactive and the loose radicals that are produced harm the DNA. All that's taking position then back the sunburn (direct DNA harm) is prevented. loose radicals reason cancer. In settlement with the lab-documents the medical records instruct an more advantageous cancer threat for sunscreen consumers compared to non-consumers. See wikipedia: "sunscreen" the in simple terms sunscreen that does no longer penetrate into the floor is Zink-oxide - yet no longer the nano-sized one. This Zink-oxide (no longer nano sized!!!) continues to be on the floor which makes it unsightly to apply, yet a minimum of it does no longer enhance your cancer threat.

Answer 6

Do you mean how long does it last laying around in the bottle? Check the expiration date. Or do you mean how long does it last while you are wearing it? Check the directions, it tells you how often to reapply.