Check the jar symbol: how to tell if your sunscreen is still effective and when to replace it

Key Highlights
Introduction
The open-jar symbol: what it is and how to read it
Why sunscreens get less effective
How expiry is shown on packaging: PAO vs best-before vs batch codes
How long do sunscreens typically last?
Real-world examples where degradation matters
Practical steps to track and preserve your sun protection
Sprays, lotions, mineral vs chemical filters — anything special to know?
Signs a sunscreen has gone bad — visual and sensory cues
How often should you replace sunscreen — a practical schedule
UV timing and seasonal use — when protection matters most
Buying and label tips — what to look for when you shop
Special considerations for travel and storage
Makeup, moisturisers and lip balms with SPF — they count too
Environmental and cost considerations
When to seek medical advice
Quick checklist: safe sunscreen habits
What consumer watchdogs and health bodies recommend
Case study scenarios — everyday decisions and consequences
Debunking common misconceptions
Buying smarter — choices that reduce the risk of degraded protection
FAQ

Key Highlights

Look for the open-jar icon with an "M" (the Period After Opening, or PAO) on the back of sunscreen and other cosmetics; it tells you how many months a product remains effective after first opening.
Sunscreens lose potency with age, heat and light; using an expired or degraded product raises the risk of sunburn, photoageing and long-term skin damage.
Practical steps — mark the opening date, store products cool and shaded, discard if texture or smell change — protect both skin and wallet by replacing sun protection at the right time.

Introduction

As Britain moves from chill to sunshine, one small symbol on the back of a bottle can make the difference between reliable protection and dangerous false confidence. The open-jar marking on many sunscreens and cosmetic containers, often followed by a number and the letter "M", is a simple consumer tool that indicates how long a product should be used after it's opened. Ignore it, and you risk applying a lotion that no longer delivers the SPF protection printed on the label.

Public-health bodies and skin specialists warn people not to assume last year’s suncream will still be effective. The product’s filters and preservatives deteriorate over time and with exposure to heat and light. That deterioration reduces the sunscreen’s ability to block or absorb ultraviolet radiation, increasing the chances of sunburn and long-term damage such as premature ageing and precancerous skin lesions.

This article explains what the PAO symbol means, how sunscreens degrade, what to look out for on packaging, how to store and handle your sun protection properly, and practical routines to ensure you never leave the house without reliable coverage.

The open-jar symbol: what it is and how to read it

The small icon that looks like a jar with an open lid and a number beside it is the Period After Opening indicator — widely abbreviated as PAO. The number, followed by the letter "M" for months, tells you how many months a cosmetic product remains safe and effective from the moment you open it.

Examples:

6M means use within six months of opening.
12M means use within 12 months.
24M means use within two years.

Brands display the PAO icon on many cosmetics, including sunscreens, moisturisers with SPF, foundations, and lip balms. If you cannot remember the exact opening date, the simplest practice is to write the date on the container with a permanent marker when you first open it. The PAO symbol gives a clear timeframe; combining that with a marked date removes guesswork.

Not all products will carry a PAO symbol. When a product’s minimum durability (for unopened items) is shorter than 30 months, manufacturers often provide a "best before end" date printed on the packaging. If neither a PAO nor a best-before date is present, err on the conservative side: assume a shorter useful life once opened and replace within a year.

Why sunscreens get less effective

Sunscreens work because their active ingredients either absorb ultraviolet (UV) radiation or physically block it. That functionality depends on chemical stability and the integrity of the formulation.

Key ways sunscreen loses effectiveness:

Breakdown of UV filters: Chemical filters such as avobenzone, octocrylene or oxybenzone can oxidise or break down when exposed to sunlight, heat or air. The product’s labelled SPF is the result of carefully tested concentrations of these filters. Over time, concentrations drop or the molecules change shape and stop delivering the tested protection.
Loss of emulsion stability: Many sunscreens are emulsions — mixtures of oil and water kept stable with emulsifiers and preservatives. Temperature swings or prolonged heat exposure (for example, leaving a bottle in a hot car) can cause separation, clumping or changes in texture that reduce spreadability and raise the risk of uneven application.
Decreased preservative effectiveness: Water-containing products rely on preservatives to prevent microbial growth. Once the preservative system becomes less effective, the product can harbour bacteria or fungi that may irritate skin and compromise performance.
Oxidation and contamination: Repeated opening, dipping fingers into a jar, or exposing the nozzle to sand and seawater introduces oxygen and microbes, accelerating degradation.

When the sunscreen no longer delivers the labelled SPF, users are more likely to burn even though they applied a product. That false sense of security is the primary hazard of using expired or poorly stored sun protection.

How expiry is shown on packaging: PAO vs best-before vs batch codes

Manufacturers indicate durability in three common ways:

PAO (the open-jar symbol with an M): This applies after opening and is the clearest guide for consumers. It answers the question: after I first open this tube, how long should I use it?
Best-before / "use-by" date: Often shown as an hourglass or a specific date on the packaging. This indicates minimum durability for unopened product. If there's a best-before date and the product is unopened, it should be safe until that date when stored properly.
Batch codes and manufacturing dates: Not visible as expiry details but printed as codes. Online tools such as batch-check websites can sometimes translate codes into manufacture dates, helping estimate an expiry if no PAO or best-before date is present.

Regulatory frameworks for cosmetics require manufacturers to provide clear durability information. For products intended to remain effective after opening (many sunscreens fall into this category), the PAO icon is the standard labelling practice.

How long do sunscreens typically last?

Shelf life depends on formulation, packaging and storage conditions. General industry patterns:

Unopened sunscreens: Typically retain their labelled effectiveness for two to three years when stored in cool, dry conditions. A best-before date printed on the tube will provide the manufacturer’s guidance.
Opened sunscreens: The PAO marking determines the official post-opening lifetime. Many cosmetic products show PAO values between six months and two years. Sunscreens commonly fall between 6M and 24M depending on ingredients and preservative systems.

If a product lacks any indication, a conservative consumer rule is to replace it 12 months after opening. When in doubt, discard. The cost of a new bottle is small compared with the health and treatment costs associated with sunburn and skin damage.

Real-world examples where degradation matters

Holiday leftovers: People often bring home almost-full tubes from summer holidays and store them for the next sun season. If that bottle was opened during a hot, sunny trip and then stowed in a warm drawer, its filters may have already degraded.
Beach bag heat: A sunscreen left all day in a hot beach bag, exposed to warm sand and fluctuating temperatures, will experience stress that accelerates breakdown.
Car glovebox or dashboard: Leaving bottles on a car dashboard or in a glovebox exposes them to high temperatures; UV filters and emulsifiers deteriorate more quickly under such heat.
Shared jars and pumps: Dipping fingers repeatedly into a communal jar at home or the gym increases contamination risk. Contaminants can destabilise preservatives, reducing both safety and effectiveness.

These common scenarios explain why the simple act of noting when you opened a bottle and how you stored it matters to protection quality.

Practical steps to track and preserve your sun protection

Mark the opening date: Use a permanent marker or a sticker on the tube to write the day you first opened it. That single habit removes the biggest source of uncertainty.
Follow the PAO or best-before date: If the jar icon says 12M, discard 12 months after the marked opening date. If there is a best-before date and the product remained unopened until that date, use or replace accordingly.
Store sensibly: Keep sunscreens in a cool, dry place out of direct sunlight. Avoid leaving them in cars, on windowsills or in hot beach bags for prolonged periods.
Avoid contamination: Use product dispensers or squeeze tubes when possible. If using a jar, consider dispensing onto your palm rather than dipping fingers into the container.
Watch for visual cues: Changes in smell, colour, texture (separation, graininess, clumping), or difficulty spreading are signs of degradation. If a product smells "off" or separates and won’t re-emulsify on shaking, dispose of it.
Reapply correctly: Even a fresh, properly stored sunscreen fails if not applied liberally. Follow recommended application amounts and reapply every two hours, and after swimming or heavy sweating.
Use batch-checking tools: If only a batch code is present, online converters can sometimes reveal manufacture dates. That information can help infer likely expiry when PAO or best-before dates are absent.

A simple rule: the combination of an initial opening-date mark plus adherence to the PAO value eliminates uncertainty and keeps protection reliable.

Sprays, lotions, mineral vs chemical filters — anything special to know?

Sprays:

Convenience encourages under-application. Spray products must be applied liberally and rubbed in for full coverage.
Aerosol and pump sprays still include active filters that can degrade with time and heat; they also can lose propellant efficiency if left in extreme conditions.
Avoid inhaling spray during application and be cautious around children.

Lotions and creams:

Thick emulsions often provide consistent feel and easier assessment of spoilage. Separation or graininess is easy to spot.
Water-based formulas require preservatives and are more prone to microbial contamination if repeatedly exposed to moisture.

Chemical filters:

Work by absorbing UV radiation; examples include avobenzone and octocrylene. Their stability can be sensitive to UV and heat; many formulations include stabilisers to improve life span.
Some chemical filters are more susceptible to breakdown over time; manufacturers counter with formulation chemistry and packaging.

Physical (mineral) filters:

Contain zinc oxide or titanium dioxide and work by reflecting/scattering UV rays. They are often considered more photostable than chemical filters.
Mineral sunscreens can settle or clump in formulations; shake or mix if separation occurs (following manufacturer guidance).

Despite these differences, the PAO and storage guidance generally apply to all sunscreen types. The margin for safety narrows when filters break down; use manufacturer instructions and the PAO marking as your primary guidance.

Signs a sunscreen has gone bad — visual and sensory cues

Sunscreen should feel smooth and mild-smelling, with consistent colour and spreadability. Discard any product that shows:

Off smell: rancid or chemical odours suggest oxidation.
Texture change: separation into watery and oily layers, graininess, clumps, or a paste-like consistency indicate emulsion breakdown.
Colour change: yellowing or darkening can signal chemical changes in filters or other ingredients.
Pack failure: a pump that sputters excessively or containers that leak after being stored properly.
Irritation on application: if a product that previously caused no reaction suddenly stings or irritates, stop using it and discard.

If you see any of these signs, do not risk prolonged use. Apply fresh protection before sun exposure rather than testing an uncertain product on an area of sensitive skin.

How often should you replace sunscreen — a practical schedule

Daily face/hand sunscreen: Replace every 12 months after opening; many daily-use facial SPFs will have a PAO of 12M or 24M. If used daily, the bottle may be finished within the year; if not, adhere to the PAO.
Holiday/full-body bottles: If you open a large bottle for a two-week vacation, write the opening date and discard according to PAO; if the PAO is 12M and you used it only briefly, it may still be safe for later use if stored correctly.
Children’s sunscreen: Replace annually, and discard immediately if the product changes in smell, colour or texture.
Lip balms and makeup with SPF: These often have shorter PAOs. Replace at least every 6–12 months, depending on the marking.
Sprays: Check PAO and best-before date; sprays are often used quickly but store them responsibly.

If you cannot determine when a product was opened and there is no PAO, a cautious approach is to replace it annually. Consumers tend to under-apply sunscreen; do not further undermine protection by using aged product.

UV timing and seasonal use — when protection matters most

Sun safety organisations recommend sun protection measures when the ultraviolet index reaches 3 or above. In the UK, that generally covers March through October, though high UV days can occur outside that window. British health bodies advise particular caution between late morning and mid-afternoon, when UV intensity peaks.

Key time-based guidance:

Protect between March and October in the UK, when the UV index frequently surpasses 3.
Be extra cautious between 11am and 3pm, when UV intensity is commonly at its highest.
Don’t rely on temperature alone. UV levels can still cause damage on cool or cloudy days.

Balancing vitamin D needs with sun protection is an individual matter. Health services advise finding a balance between getting short, safe sun exposure for vitamin D where appropriate and avoiding enough exposure to cause burning. For specific guidance about vitamin D and sun exposure based on age, skin type and health, consult your health service or a clinician.

Buying and label tips — what to look for when you shop

Check for PAO and best-before marks before buying, especially if you purchase during off-season sales or from discount sellers.
Prefer sealed products: buying unopened bottles from reputable retailers reduces the risk of prior heat damage or tampering.
Read the label for water resistance claims if you need protection while swimming or exercising. Water resistance does not mean "waterproof"; reapplication after swimming or towelling is still necessary.
Avoid very cheap or bulk suppliers without clear labelling. Cost concerns are valid but not at the expense of proper protection.
Consider travel-sized tubes for infrequent users to reduce the risk of product sitting unused for long periods.
Watch for batch codes that look smudged; illegible codes can make tracking expiry difficult.

Brands that list both a best-before date and a PAO offer the clearest guidance. Keep product packaging long enough to consult the label when needed.

Special considerations for travel and storage

Flights and airports: Pack a travel-sized, unopened sunscreen in checked luggage or follow airline and security rules for liquids in carry-on. Unopened bottles are more likely to retain potency.
Beach trips: Carry sunscreen in a shaded compartment of your beach bag and avoid leaving it on the sand or in direct sunlight.
Car storage: Never leave sunscreen on a dashboard or a hot car seat for extended periods. Heat accelerates chemical breakdown.
Hotel rooms and holiday rentals: Store bottles in a cool, shaded place; do not assume the accommodation will be air-conditioned or cool.

For frequent travellers or those who use sunscreen only in summer, buying smaller tubes each season and discarding them at season’s end may be the most reliable approach.

Makeup, moisturisers and lip balms with SPF — they count too

Many people rely on moisturisers and makeup with built-in SPF for daily protection. Those products are still subject to the same PAO and best-before rules. Keep these points in mind:

Amount matters: Cosmetic products that contain SPF often do not deliver the labelled protection unless applied at the same thickness used in SPF testing. The amount you actually use daily is usually less than the laboratory-tested amount.
Replace regularly: Foundations and moisturisers with SPF degrade; mark them with an opening date and stick to the PAO.
Lip balm SPF: Lip products face particular contamination risk because of contact with the mouth. Replace lip balms with SPF every 6–12 months and discard if there is a taste change, texture change or visible contamination.

Using a dedicated sunscreen for high-risk sun exposure (beach, prolonged time outdoors) and relying on SPF makeup for incidental protection is a sound approach.

Environmental and cost considerations

Throwing away partially used suncream feels wasteful, but expired or degraded sunscreen can give a false sense of security. Consumers can reduce waste while maintaining protection by:

Buying sizes that fit usage patterns — smaller tubes for infrequent users, larger for families.
Using travel-size bottles for seasonal trips rather than keeping a single bottle for years.
Sharing responsibly: do not double-dip into jars or share lip products.
Recycling packaging where local facilities allow. Rinse tubes and pumps according to local recycling guidance; check brand recycling schemes when possible.

A safety-first approach combined with smarter purchasing reduces both health risk and unnecessary waste.

When to seek medical advice

If you develop an unexplained skin reaction such as a rash, persistent redness, swelling, or signs of infection after applying sunscreen, stop using the product and consult a healthcare professional. If you experience repeated sunburns despite using sunscreen properly (generous application and reapplication), seek advice on appropriate protection strategies and skin checks. Precancerous spots or suspicious moles warrant evaluation by a dermatologist.

Quick checklist: safe sunscreen habits

Look for the PAO jar icon and write the opening date on the bottle.
Replace according to the PAO or best-before date; if neither is present, default to replacing within 12 months after opening.
Store sunscreen cool, away from direct sunlight and avoid letting it sit in a hot car or on a windowsill.
Apply sunscreen liberally and reapply at least every two hours, and after swimming or heavy sweating.
Watch for signs of spoilage: changes in smell, texture or colour.
Use dedicated sunscreens for extended outdoor exposure rather than relying only on cosmetics with SPF.
When traveling, pack sunscreen in carry-on if you’ll need it on arrival, and buy smaller tubes if you use suncream infrequently.

What consumer watchdogs and health bodies recommend

Consumer groups and health organisations emphasise the importance of using effective sunscreen and being aware of expiry and storage. In practical consumer guidance:

The Which? consumer group highlights the PAO symbol and recommends writing the opening date on the container.
Cancer Research UK and the British Association of Dermatologists advise taking sun safety measures when the UV index reaches three or above, typically between March and October in the UK.
The NHS stresses balancing sun protection with vitamin D needs, while warning that sunburn increases risk of skin cancer and can occur on cloudy days.

These organisations converge on straightforward, practical steps: use adequately tested sunscreen, check its durability, and apply it correctly when risk of UV exposure is substantial.

Case study scenarios — everyday decisions and consequences

Scenario 1: The forgotten bottle Anna keeps a half-used SPF 30 lotion from last summer in a kitchen cupboard. She finds it the following spring and uses it during sunny afternoons. She notices a slight sunburn after an outing. The likely cause: the lotion’s filters declined in potency during storage and use, giving less protection than its label indicated. Marking the opening date and following the PAO would have prevented this risk.

Scenario 2: The beach bag mistake Tom leaves a tube of sunscreen in a zipped beach compartment all day, exposed to high temperatures. He uses the same tube on subsequent days. Heat accelerated chemical breakdown and emulsion instability; the product’s ability to deliver tested SPF fell. He experiences patchy coverage and a sunburn despite reapplication.

Scenario 3: Shared jar at the gym A small gym offers a communal jar of SPF moisturiser. Multiple users dip fingers into the jar regularly; water or sweat contaminates the product. Over time, microbial growth leads to irritation for some users. Contamination risk is one reason pump or tube packaging is preferable for public or shared settings.

These everyday situations show how small habits affect protection.

Debunking common misconceptions

Myth: If it looks okay, it must be fine. Appearance can be misleading; reduced SPF may not show obvious visual cues. Always check PAO and discard by the recommended date.
Myth: Sunscreen only matters on hot days. UV radiation can harm skin on cool or cloudy days; protection matters when UV index is 3 or above.
Myth: Higher SPF lasts longer. SPF reflects sun protection per application, not the chemical longevity of a product. A high SPF product still degrades with time, heat and exposure.
Myth: Unopened bottles never expire. Unopened products do have a best-before date and can degrade if stored in poor conditions (heat, humidity).

Clearing these up helps people make safer choices.

Buying smarter — choices that reduce the risk of degraded protection

Choose formulations with clear PAO and best-before labelling.
For infrequent users, opt for travel-sized tubes to avoid long periods of sitting half-used.
For families, buy larger quantities with secure pump dispensers to minimise contamination and waste.
Check retailer storage habits for clearance or discounted products; avoid items that may have been kept in hot or exposed environments.

A bit of attention at purchase prevents problems later.

FAQ

Q: What does the jar symbol with an "M" mean? A: That icon is the Period After Opening (PAO) mark. The number followed by "M" indicates how many months a product should be used after opening. For example, 12M means use within 12 months of first opening.

Q: Can I use last year’s sunscreen if it looks okay? A: Do not assume skin protection remains the same. Even if the lotion looks and smells acceptable, its UV filters may have degraded. Check the PAO or best-before date and the opening date you marked. If uncertain, replace it.

Q: How long does sunscreen last unopened? A: Many unopened sunscreens remain effective for two to three years if stored properly. Look for a best-before date on the packaging. Store unopened bottles in cool, shaded conditions.

Q: How long does sunscreen last after opening? A: The PAO determines post-opening life. Many cosmetic products show PAOs from 6 months to 24 months. If no PAO is marked, consider replacing within 12 months after opening.

Q: Are mineral sunscreens more stable than chemical ones? A: Mineral (physical) filters like zinc oxide and titanium dioxide are generally more photostable than some chemical filters, but any formulation can degrade with heat, contamination or age. Follow the PAO and storage guidance regardless of type.

Q: If the sunscreen separates but isn’t smelly, can I shake it and keep using it? A: Some separation in emulsions is reversible with vigorous shaking, but repeated separation can indicate instability. If the texture or spreadability is altered or if it separates persistently, discard and replace.

Q: Does sunscreen expire if left in a hot car? A: Prolonged heat accelerates chemical breakdown and emulsion failure. Avoid leaving sunscreen in cars or other hot environments. Even one extended heat exposure can reduce effectiveness.

Q: What if the product has no PAO and no best-before date? A: If you cannot determine durability, a conservative rule is to replace the product within 12 months after opening. Consider using smaller packaging or buying a fresh tube each season.

Q: How much sunscreen should I apply and how often? A: Apply generously and evenly to all exposed skin. Reapply at least every two hours, after swimming and after heavy sweating or towelling. Ensure you cover ears, the back of the neck and hands. When in doubt, reapply.

Q: Can I rely on moisturiser or makeup with SPF for beach days? A: Cosmetic products with SPF provide some protection but often not at the thickness used in SPF testing. For prolonged outdoor activity, use a dedicated sunscreen with appropriate SPF and water resistance rating, and reapply as needed.

Q: How should I store sunscreen at home? A: Keep sunscreen in a cool, shaded place away from direct sunlight and avoid extremes of temperature. Do not leave bottles on windowsills or in hot cars. Close caps tightly after use.

Q: What are signs a sunscreen has gone bad? A: A change in smell (rancid or chemical), colour change, separation that won’t resolve, grainy or lumpy texture, and skin irritation upon application are indicators to discard the product.

Q: Can I check the manufacturing date from a batch code? A: Some online batch-code checkers translate manufacturer codes into manufacture dates, enabling you to infer expiry. Use reputable batch-check sites and cross-check with the product’s PAO or best-before information.

Q: How can I reduce waste while ensuring effective protection? A: Buy sizes suited to how often you use sunscreen, use travel-size bottles for occasional trips, mark opening dates to avoid unnecessary hoarding, and replace products according to PAO or best-before dates.

Q: Who should I contact if I get a bad reaction to sunscreen? A: Stop using the product immediately and consult a pharmacist or healthcare professional. If symptoms persist or you suspect an infection, contact your GP or dermatologist.

Q: Does the NHS or Cancer Research UK say when to use sunscreen? A: Health bodies recommend protective measures when the UV index is 3 or above; in the UK, that typically covers March to October. Take particular care between late morning and mid-afternoon when UV intensity is higher. Balance sun exposure for vitamin D needs with the need to avoid burning; seek specific medical advice for personal guidance.

A small habit — writing the opening date on the side of a tube — preserves the value of the protection inside. The PAO icon is a consumer-friendly tool: use it. Safe, consistent application of fresh, appropriately stored sunscreen protects skin today and reduces the risk of damage years down the line.