How long can "sunscreen" be used after opening? Can the "sunscreen" opened last year still be used this year?
From the perspective of formula, the shelf life of a sunscreen product mainly depends on four aspects: 1. The stability of the sunscreen after opening; 2. The stability of the sunscreen paste; 3. Whether it will be infected by microorganisms after opening, in layman's terms, whether it will be contaminated with bacteria; 4. The stability of other ingredients. Zhen Yao will analyze these four aspects in detail to see how long the "sunscreen" can last after opening?
Stability of sunscreen
"Sunscreen" as the core ingredient of a sunscreen product directly determines the sunscreen ability of this product. Compared with other raw materials, there are not many types of "sunscreen". There are about 53 types of sunscreen approved for use in the world, and our country has approved about 28 types of sunscreen.
"Sunscreen" can be divided into two categories: physical sunscreen and chemical sunscreen. There are very few types of physical sunscreens, and commonly used ones are titanium dioxide and zinc oxide. These two sunscreens are highly inert and stable in nature. They can remain stable even in extreme exposure environments and will not decompose or denature. Therefore, the claim that the sunscreen ability of "physical sunscreens" will decrease and be oxidized and deteriorate after opening is not valid.
We are looking at chemical sunscreens. After chemical sunscreens absorb ultraviolet rays, the electrons in the molecules jump from low-energy orbits to high-energy orbits to achieve the purpose of sun protection. Some chemical sunscreens, such as avobenzone (butyl methoxydibenzoylmethane), have poor photostability and will degrade after exposure to light, losing the ability to absorb ultraviolet rays.
It should be noted here that this type of chemical sunscreen will only decompose easily after exposure to sunlight, not oxygen. As long as the sunscreen products we use daily are not placed in high temperature and sunlight, the stability is still good and will not decompose and lose the sunscreen ability.
In addition, for some chemical sunscreens that have good sunscreen ability but are not very stable, cosmetics companies have developed many compound stabilization technologies, and the stability of sunscreens is no longer a problem. For example, Neutrogena's patented formula technology uses octocrylene and avobenzone, which makes avobenzone much more stable. L'Oreal has developed patented ingredients Mexoryl SX and Mexoryl XL, which have excellent photostability; the successful development of diethylhexyl butyramido triazone (DHHB) has improved its photostability and UVA protection.
In summary, the stability of sunscreens is still guaranteed. Even unstable chemical sunscreens can remain stable for a long time with the support of multiple compounding technologies, as long as they are not placed in high temperature and sunlight environments for a long time, and the lid is closed immediately after opening and use. The sunscreen will not decrease in sun protection ability. Some scholars have conducted experiments and compared the sunscreens that have been opened for one year with the sunscreens that have just been opened.
From the perspective of sunscreens, as long as the storage environment is in place, sunscreen products that have been opened for one year can be used. Of course, if sunscreen products are placed in a high temperature environment for a long time, such as placing sunscreen in a car in summer, the high temperature will have an effect on chemical sunscreens and affect their sun protection ability. The lighting in the bathroom has basically no effect on sunscreens.
The stability of the paste
The stability of the sunscreen paste also has a great impact on the sun protection ability of the product. If the paste is unstable, the sunscreen will be stratified and precipitated, which will directly affect the film-forming property of the sunscreen and greatly reduce its sun protection ability.
When a formulator develops a product, in addition to efficacy, safety and stability are one of the important considerations. Products produced by regular manufacturers will be tested in extreme environments before they are put on the market to test the stability of the products. Unstable products cannot pass the test. Products that can pass the test generally have no problems with stability. Product stability is the most basic requirement for a formulator.
As long as the sunscreen is produced by a regular manufacturer, under normal use conditions, there will be no problem with stability one year after opening. Of course, when consumers use products that have been placed for a period of time, they can also observe it themselves. If the paste shows stratification, precipitation, oil-water separation and other phenomena, it means that the stability of the paste has been destroyed, so don't use it anymore.
Before a product is launched on the market, antiseptic ability is one of the indicators that must be tested in various tests. Only products that pass the antiseptic ability test will be approved for listing. Antiseptic ability is one of the factors that must be considered when designing a formula. If the irritation to the skin is not considered, the existing antiseptic technology is already very perfect. As long as the lid is changed immediately after opening and the paste is not exposed to the air for a long time, it will be fine to store it for a year, and the microorganisms will generally not exceed the standard.
Stability of other ingredients
In addition to the main ingredients mentioned above, sunscreens also add some moisturizers, emollients, antioxidants, plant extracts, etc. These ingredients mainly play an auxiliary role in the entire formula system. Many sunscreens have some high-end ingredients, but the amount of added is very small. They are mainly hyped as a gimmick, and the actual significance is not great, so they can basically be ignored.
Even if some ingredients with auxiliary effects are well preserved, the effect on their characteristics after one year is very small and very limited. There is basically no effect on the sunscreen ability of sunscreen.
Judging the shelf life based on the label
Some products will indicate the shelf life after opening on the outer packaging. You can look for it on your product carton or bottle. If the following logo appears:
6M means the shelf life after opening is 6 months and it must be used up within 6 months; 12M means the shelf life is 12 months and it must be used up within 12 months. You can follow this. Some products do not have this logo. If it is a sunscreen, you can judge it based on the content of this article.
In summary, the shelf life of sunscreen after opening depends on the user's storage environment. If it is in a light-proof, low-temperature, and airtight environment, cover the lid immediately after use, and it will be fine to store it for one year. Last year's sunscreen can still be used this year, don't worry. If the user is not careful, it may not be usable after half a year. For consumers who pay more attention to sun protection, a bottle of sunscreen can be used for about 2 months, so this problem does not exist at all!
Glass Makeup Bottle
