I’m about to tell you something you’ve definitely heard before. Yeah, yeah, it’s about wearing sunscreen in winter.

Just because you’re not spending your days lying on the beach or covered in sweat (oh, was that just me?), doesn’t mean the sun isn’t damaging your skin and increasing your skin cancer risk.

The message is clear: make putting on sunscreen part of your morning routine. Choose a broad-spectrum sunscreen that’s SPF 30 or higher and apply to your face and all areas of your skin not covered by clothing. Why though?

In Queensland, the UVR Index is above three for the majority of the day all year round (even winter), meaning you’ll need to use a combination of sun protection behaviours, including sunscreen, whenever you’re heading outside. Rant over.

We’ve all heard it time and time again. Just like we’ve all had the ‘slip, slop, slap, seek, slide’ sun-safe behaviours song stuck in our heads since primary school.

(Quick recap if you missed it: slip on protective clothing, slop on sunscreen and slap on a wide-brimmed hat, seek shade and slide on some sunnies). But what if the sunscreen you’re planning on slopping on has expired?

It's true. Like a near-empty bottle of milk or the chicken you bought but forgot to cook, sunscreen can go off.

Keep reading for exactly where to find your sunscreen's expiry date, why it's important, how to tell if yours has gone off and the best ways to store sunscreen to get your money's worth.

Does sunscreen expire?

Why, yes. Yes it does.

The short version is: sunscreen contains a combination of chemicals or active ingredients that work to protect you from the sun. Over time, these chemicals and ingredients degrade and therefore can't do their job to the full extent listed in the job description.

According to Kaye Pulsford, the Executive Director of Queensland Health's Preventive Health Branch, "Sunscreen that has passed its expiry date will not provide the same level of ultraviolet radiation (UVR) protection as is intended and can increase your chance of getting sunburnt".

Pulsford added that in Australia, the Therapeutic Goods Administration (TGA) has specific regulatory requirements that sunscreen labels must have to safeguard Australians who use them.

"Having an expiry date is one of those regulatory requirements," Pulsford told Mamamia.

Thankfully, sunscreen doesn't go off quite as quickly as milk in the fridge. The TGA have some of the strictest sunscreen testing standards in the world, and each product is rigorously tested to ensure it provides the SPF level stated on the bottle for the shelf life of the product.

Where to find the use-by-date on your sunscreen.

The TGA requires all sunscreens to have an expiration date printed on the bottle to indicate how long it will be effective for.

"The expiry date is usually provided with the active ingredients and recommendation on storage - on tubes of sunscreen, the expiry date is usually printed on the sealed end of the tube," Pulsford said.

You can bank on the fact every sunscreen bottle will have an expiry date, but unlike milk cartons, you won’t always find them in exactly the same spot. Sometimes it’ll be on the bottom, sometimes it’ll be on the very top, sometimes it’ll be somewhere in the middle, on the back or the front. It’s not always obvious, which is why it’s so easy to miss. You just have to look carefully.

If you can't find an expiry date, some sunscreens label the manufactured date instead, which you can add three years onto to get the use-by date.

For example, manufactured dates often look like this: YYDDD (year, day of the year). So if the code shown on your bottle was 19031, it would mean that product was manufactured on 31 January, 2019.

How to tell if your sunscreen has expired?

Sorry to keep bringing up milk, but expired sunscreen isn't all that different to an expired bottle of milk. OK, it's not thaaaaat bad, but bad enough to not put it on your skin or anyone else's.

Things to look out for in expired sunscreen:

• Watery consistency.
• Separation of emulsion.
• Graininess.
• Colour and/or odour changes.
• Clumping or pilling.

Long story short - if your sunscreen doesn't look or smell like it did when you bought it, there's a good chance it's off.

How long does sunscreen last for before it goes off?

Technically speaking, many sunscreens last up to three years. But that's assuming you'll never take your sunscreen anywhere fun, like the beach, to the park or anywhere in the outside world.

Factors like sun and heat can speed up your sunscreen's expiry - for example, keeping it in a beach bag all day or always storing your sunscreen in your handbag could reduce its effectiveness. By using sunscreen, you're also exposing the product to bacteria from your hands and the outside world, which can impact on the effectiveness.

But don't fret, because the aim is to use up all that hard working, protective sunscreen long before it ever goes off.

A great rule of thumb is: if you reach for a sunscreen in the depths of your bathroom cabinet and you can't remember when you bought it, replace it.

How to store sunscreen.

This one's easy.

"Sunscreen should be stored in a cool, dry place out of direct sunlight; that is below 30 degrees. So keeping a bottle in the glove box of the car is not recommended," Pulsford said.

That doesn't mean you can't or shouldn't take sunscreen with you to the beach, but try and store it out of direct sunlight and in the shade if you can, and pop it back in the cupboard when you're done instead of leaving it in the car for next time. If you've got a cool bag or an esky with you, they're both good places to store it.

Other sunscreen tips to keep you protected.

Now you know why it's important to use sunscreen that's in date, how to find the expiry date on your sunscreen, and how to tell if yours has gone off, here are some extra tips from Queensland Health's Feel Good Facts resource on the best way to apply it make sure you're fully protected:

• Sunscreen should be applied 20 minutes prior to going outside, and should be reapplied every two hours and more frequently if swimming or sweating.
• Reapply every two hours, for both physical and chemical sunscreens (chemical sunscreens filter and absorb UV rays to prevent them from damaging your skin, and physical sunscreen act as a barrier and bounce the rays back into the environment).
• The SPF rating of the sunscreen refers to the level of UVA rays and UVB rays that are blocked or filtered when sunscreen is applied in accordance with the manufacturer’s directions. The higher the SPF number, the higher the protection against sunburn. According to the Cancer Council, SPF30+ allows 3.3% of UVR to reach your skin, while SPF50+ allows 2 percent to get through - and yes, that's still something.
• So, this doesn't mean very high rating SPF sunscreens (like SPF 50+) are a suit of armour - you still need to reapply and take other sun safety measures like seeking shade and wearing protective clothing and a broad-brimmed hat.
• Always read the instructions, and apply generously - most people don't apply enough, you need a teaspoon for the face, neck and ears; a teaspoon for each arm and leg, and a teaspoon each for the front and back of the body. Ideally, your sunscreen wouldn't get the chance to expire if you're using it as per instructions.

Now, what are we going to do this winter? Check our sunscreen expiry date and wear it every day.

Class adjourned.

For more information about sun safety, especially protecting yourself in the Queensland sun, visit Queensland Health Feel Good Facts.