If there's one skincare rule that deserves to be sacred, it's this: using sunscreen every day is one of the best anti-aging strategies out there. More effective than any serum or cream with trendy ingredients. But with the arrival of a new season of sun and outdoor living, many people are still using last year's sunscreen, unaware that it could be doing more harm than good.
A recent survey conducted by SAFE in five countries with over 6,000 participants revealed that 57% of people admit to using the same sunscreen year after year. This figure is not only concerning; it's a clear sign that many of us are ignoring the science behind SPF. Sunscreen, like any other cosmetic, has an expiration date. And when that date passes, so does its protective ability.
Here's why using last year's sunscreen is a mistake – and what you need to know to keep your skin protected this summer.
Your sunscreen isn't forever – and neither is its protection
Sunscreen is formulated with active UV filters, emulsifiers, emollients, preservatives, and other functional ingredients. All of these work in synergy to absorb or reflect the sun's ultraviolet radiation, protecting the skin from premature aging, sunburn, hyperpigmentation, and potentially skin cancer.
But, like any cosmetic product, sunscreen degrades over time. Once opened, the countdown begins: exposure to oxygen, light, heat, and even your own fingers can gradually diminish its effectiveness.
So when you use last summer's sunscreen, even if it looks fine, you're applying a product whose protection is no longer reliable.
Ingredient degradation: A silent breakdown
One of the most important reasons not to use last year's sunscreen is the degradation of its active ingredients, especially UV filters.
What many people don't realize is that formulating an effective and stable sunscreen is extremely complex. UV filters – whether chemical or mineral – are notoriously difficult to incorporate. They're not added like a perfume or a botanical extract; they completely change the product's structure and behavior. And they often make the formula more prone to instability, separation, or degradation over time.
Chemical filters
Chemical filters like avobenzone, octinoxate, and oxybenzone work by absorbing UV rays and converting them into heat. But they are very unstable. For example, avobenzone begins to degrade when exposed to the sun if not carefully stabilized with ingredients like octocrylene. And if stored in a warm place, such as a beach bag or next to a sunny window, these filters can deteriorate significantly, rendering the product unreliable.
Mineral filters
Mineral filters like zinc oxide and titanium dioxide are generally more photostable, but they present their own challenges. They are not simple ingredients: they are high concentrations of powders that must be homogeneously dispersed in an emulsion. This requires advanced formulation techniques and special coatings to ensure long-term stability. If they are not correctly coated or the formula becomes destabilized, they can cause photocatalytic reactions when exposed to the sun, generating free radicals that degrade the oils, emulsifiers, and antioxidants in the formula.
In summary, sunscreen is one of the most difficult cosmetic products to formulate and also one of the most vulnerable to the passage of time, heat, and exposure.
The expiration date exists for a reason
All sunscreen sold in the EU must comply with strict cosmetic regulations, including an expiration date or PAO (Period After Opening) symbol. This small icon – an open jar followed by “6M” or “12M” – indicates how many months the product remains safe and effective after opening.
For example, if your SPF50+ moisturizer indicates 12M and you opened it last April, it has now expired. This means the manufacturer can no longer guarantee its effectiveness, and using it could leave your skin dangerously exposed.
Remember: the PAO starts counting from the first opening, and assumes ideal storage conditions. High temperatures – such as in a beach bag, car glove compartment, or even in the bathroom during the summer – accelerate degradation and can significantly shorten that period. If the product is unopened, look for the expiration date printed on the packaging. In any case, the clock starts ticking from the product's manufacturing date.
Poor storage accelerates degradation
Even if the date on the packaging indicates that your SPF is still in good condition, the way it has been stored greatly influences its actual stability.
Leaving it in the car, exposing it to direct sunlight, or storing it in a humid bathroom causes thermal and light instability. Heat can cause the emulsion to separate, oils to go rancid, and UV filters to degrade rapidly.
This is especially true for natural or mineral sunscreens, but it also applies to any SPF formula. Once it has been subjected to fluctuating temperatures or is not properly sealed, it is no longer a product you can trust, regardless of the brand.
Uncertain protection = Increased risk
There's a dangerous myth that if a sunscreen hasn't changed color or smell, it's still good. But that's not true. Unlike spoiled food, an expired SPF doesn't always show visible signs.
The real problem is that you no longer know how much protection you're getting. What was once SPF50 may have been reduced to SPF20. Or less. This creates a false sense of security and can increase the risk of sunburn, DNA damage (to skin cells), pigmentation, wrinkles, and long-term skin deterioration.
Applying last year's sunscreen may seem responsible, but in reality, you could be completely unprotected.
The hidden risk: Irritation and allergic reactions
As sunscreen ingredients degrade – especially from sunlight, heat, and oxygen – their chemical composition changes. This can lead to unexpected skin reactions, even if you previously tolerated it well.
Expired or poorly stored sunscreen can become contaminated, unstable, or cause irritation, especially on sensitive or reactive skin. Perfumes can oxidize, oils can go rancid, and preservatives can fail. The result? Redness, stinging, rashes... all caused by a product that was supposed to protect you.
Chemical vs. Mineral: Which degrades more?
It's a common myth to think that mineral sunscreens don't expire. While chemical filters degrade more easily if not well-stabilized, mineral sunscreens also face stability challenges.
Filters like zinc oxide and titanium dioxide are more resistant, but maintaining a uniform and stable dispersion of these particles, especially in high concentrations needed for high SPFs, is complicated. When exposed to the sun, these particles can also cause reactions that degrade other ingredients if they are not well-stabilized.
Although antioxidants and emulsifiers help, no formula is designed to last indefinitely, and certainly not from one year to the next.
What about hybrid sunscreens?
Hybrid sunscreens, which combine chemical and mineral filters, present an added complexity. Some research suggests that zinc oxide can interact with and degrade certain chemical filters, further complicating their long-term stability.
That's why many formulators choose to use separate filters or create formulas with advanced emulsifiers and emollients. But even so, freshness remains key.
How to tell if your sunscreen has expired
Wondering if you can still use last year's sunscreen? These signs indicate it's time to say goodbye:
- It has separated, become liquid, or has lumps.
- It has a rancid or sour smell.
- It has changed color.
- The expiration date or PAO has passed.
- It has been exposed to heat or sun.
- It causes irritation or stinging when applied.
When in doubt, stop using it. Your skin deserves better than uncertainty.
How to store your sunscreen to make it last longer
- To get the most out of your SPF during the season:
- Store it in a cool, dry place, away from heat sources.
- Keep the container tightly closed to prevent air and moisture from entering.
- Protect it from direct sunlight: wrap it in a towel or store it in a portable cooler at the beach or pool.
- Check the expiration date and note the opening date if needed.
- Use it generously and reapply every two hours. This ensures good protection and you'll finish it before it expires.
The best way to avoid relying on last year's sunscreen is to use it consistently and liberally. And if you have some left at the end of your vacation or the season, don't keep it: share it with the person next to you on the beach or by the pool. Everyone deserves to be well protected, and that way you ensure it's used before it loses its effectiveness.
Don't play with your skin's health
At Twelve Beauty, we believe skincare should be effective, honest, and safe. That's why we formulate our SPF Artemisia Power Protection Moisturiser SPF50+ and its tinted version with non-nano, uncoated mineral filters, safe for sensitive skin and the environment. But even the best formulas must be used within their shelf life. No SPF – not even ours – is immune to the passage of time, heat, or exposure.
Conclusion
Sunscreen is not a product to hoard. It's a product to use. The sun doesn't take vacations, and neither should your SPF. But to keep your skin healthy, radiant, and protected, you need to work with a fresh and effective formula. Last year's sunscreen might still be in your cabinet, but what it promises on the label is no longer true.
If you're serious about protecting against aging, sunburn, or sun damage, start each season with a new bottle. Choose quality mineral filters. Store it correctly. And most importantly, use it daily.
Your skin will thank you – this year and all the years to come.