In the middle of the second world war, a Swiss chemist called Franz Greiter experienced a nasty sunburn while climbing a mountain. This inconvenience inspired him to invent a product that would change the face of outdoor health and cosmetic beauty forever: the first modern sunscreen.

Greiter's miracle cream wasn't the first ever sunscreen, as sun damage has existed for as long as humans have walked the earth. The ancient Greeks used olive oil to protect their skin from the sun and as a moisturiser for when they had too much sun (interestingly, modern testing of olive oil confirms it has an SPF rating of 8!) [1][2].

In 1956, Australian mathematician Henry Lancaster published his findings about the strong and dangerous link between sun exposure and skin cancer [3].

Since then, sunscreens have advanced in application styles and textures: there are pump bottles, roll-ons, oils and sprays. There are sunscreens for sensitive skin, sporty types, swimmers, kids and babies too.

You may think that if you've applied sunscreen under your makeup in the morning, you'll be good to go for the whole day. But, this isn't true.

Wearing sunscreen every day and reapplying it is vital for ensuring your skin is protected throughout the day. We've all been guilty of forgetting it, or believing we do not need it — especially those of us who work indoors.

But, if you sit by a window at work, or go out in the car for 30 minutes, or walk your dog — you need to examine your sunscreen routine.

What is SPF?

Our friend Franz Greiter not only invented modern sunscreen but he also invented the SPF rating. SPF stands for "sun protection factor" and is the world standard measure used to understand the strength of our sunscreen. But what does it actually mean?

The official definition remains the same as it did from the 1930s: SPF is “the ratio of UV energy needed to produce a minimal erythemal dose on protected to unprotected skin" [4].

Sunscreen provides protection from the 2 types of UV rays: UVA and UVB. The latter is the ultraviolet rays that contribute to sunburn, and in the long term, skin cancer.

The most effective sunscreens offer "broad spectrum protection", meaning they will protect you against UVA and UVB rays. Be sure to look for the broad spectrum protection label on sunscreen products before purchasing them.

What strength SPF should I use?

In Australia, the lowest form of SPF you’ll find in sunscreen is SPF 15, which blocks 93% of the UV rays hitting your skin. Even though this is the lowest SPF available, it still makes a massive difference in sun protection compared to having no sunscreen.

The next level up is SPF 30, which blocks 97% of UV rays, and then a rating of SPF 50 will protect 98% of your skin. This might not seem like a massive difference between SPFs in terms of their sun protection percentage, but it does make a noticeable difference in how many UV rays will be hitting your skin.

Ultimately, your choice of SPF rating should come down to how much time you are spending in the sun combined with your skin fairness. If you have fair skin and you spend only a little time outdoors each day, then an SPF of 15 or 30 will probably be enough.

But, if you have darker skin, an SPF 15 will be highly effective. If you spend a lot of time outdoors and usually work up a sweat, an SPF 50 is recommended. This article contains a helpful chart that can help you determine which level of SPF you should be using.

How long does sunscreen last on the skin?

Guess what? Turns out we should all be reapplying sunscreen more often than we think.

Sunscreen should be on our skin whenever the UV level is above 3 and then reapplied throughout the day, especially if you are spending time outdoors.

How often should you reapply sunscreen?

Across the board, scientists and dermatologists collectively agree that sunscreen should be reapplied every 2 hours if you are outdoors or exposed to the sun, and at least 20 minutes before you step outside.

The 2-hour window should be noted irrespective of the water resistance of the sunscreen — swimming, sweating or towel drying can reduce its effectiveness.

Don't forget that reapplying sunscreen is necessary even if you're inside. If you sit next to a large window in your office, the UVA radiation has a long wavelength that can penetrate through glass.

Do I need to reapply if I work indoors?

If you work in a basement or a room with little sunlight, then Johns Hopkins University believes that you probably don't need to reapply throughout the day, but that you should remain mindful of your outdoor time [6].

Sometimes, plans change and we end up outside: how long will you be spending outside for that office fire drill? What about when you meet a friend for drinks in a beer garden after work? Unprotected exposure can happen even amongst the most organised of us, and all sun exposure is dangerous regardless of your skin type.

Keeping some small bottles of broad-spectrum sunscreen products for the face and/or body in your bag or desk at work will do the trick for those moments when you're getting some surprise sun.

Wearing sunscreen should be a major part of our morning routines and, if you have any exposed skin to direct sunlight, part of your morning, lunch and afternoon routines too!

How much sunscreen do I need?

To get full SPF broad-spectrum protection, sunscreen must be applied correctly. It might seem like common sense that you will need to apply sunscreen liberally and evenly over all your exposed skin but most of us tend to under-apply our sunscreens.

If it's under-applied, you won't be getting the SPF level benefit and will be exposing yourself to the sun's rays and skin damage.

According to the Cancer Council, the recommended amount for application is 5mL (approximately 1 teaspoon) for each arm, leg, body front, body back and face (including neck and ears) [7]. That equates to a total of 35mL (approximately 7 teaspoons) for a full-body application.

That may seem like a lot, but any board-certified dermatologist worth their salt will agree: the more the merrier. And, we cannot stress this enough, please reapply sunscreen every 2 hours.

Should sunscreen be used before or after other products?

Sunscreen should be the last step in your morning skincare routine. So, after you've cleansed, and applied a serum and moisturiser, it's then time for your sunscreen product.

Software’s Daily Sun Defence SPF50+ is designed for sensitive skin and acne-prone skin, doesn’t clog your pores and is fragrance-free. Our formula can aid in the prevention of premature skin ageing, sunspots and solar keratosis.

Try to let your sunscreen sit for 3-5 minutes before going in with makeup so it has time to sink into the skin. If you don't wear makeup, consider that your last step and you're good to go.

Most sunscreens today tend to have a moisturising component, whether you're using chemical or mineral sunscreens, making them helpful for dry skin, so some people don't feel the need to use moisturiser and sunscreen in the same routine but that's up to you.

Remember: makeup is not enough to protect your skin — even if your foundation or lipstick has a high SPF rating.

Should I use chemical sunscreens or mineral sunscreens?

Mineral or physical sunscreens are often touted as the best for delicate skin or if you are acne-prone. These sunscreens contain active ingredients like zinc oxide or titanium dioxide and form a physical barrier that reflects the light rays away from the skin (which is why they are also known as "physical" sunscreens).

The American Academy of Dermatology recommends using a good non-comedogenic formula mineral sunscreen, rather than a chemical sunscreen, if you have sensitive or acne-prone skin [6].

Chemical sunscreens, on the other hand, contain ingredients like oxybenzone, avobenzone, octisalate, octocrylene, homosalate, or octinoxate [6]. Chemical sunscreens are lighter, sheerer and tend to be favoured by people more for being easier to use.

The key difference between mineral and chemical sunscreens is that mineral/physical sunscreens sit on top of the skin and block rays at the surface while chemical sunscreens absorb rays like a sponge.

Mineral sunscreens are not necessarily better for your skin than chemical sunscreens: it depends on your skin type.

Your dermatologist will have more recommendations on which sunscreen works best for your skin type, but at the end of the day, they will be pleased with whichever sunscreen is going on your face and body every day.

Whatever product you're using each day, be sure to double-check that your sunscreen hasn't expired as this doesn't offer as much protection.

Are sunscreen products all I need for sun protection?

No! Absolutely not!

Sunscreen is only one important factor in your skin protection routine, especially if you are planning a day outdoors. When in doubt, remember the 5 S's: slip, slop, slap, seek, slide.

1. Slip on some sun-protective clothing.
2. Slop on a broad-spectrum sunscreen that's either mineral or chemical depending on your preference.
3. Slap on a wide-brimmed hat.
4. Seek shade! Put up your beach umbrella or sit under a verandah where you can.
5. Slide on your sunnies to keep UVA rays off your eyeballs. You can't apply sunscreen to your eyes, but that doesn't mean your eyes aren't vulnerable to UV damage.

Everyone should be mindful of these 5 steps not only while having a day out in the sun, but every time you leave the house.

How to reapply sunscreen over makeup

It might seem counterintuitive, but you certainly can reapply sunscreen over your makeup!

The trick to applying sunscreen to a face of makeup without smudging your foundation is blotting. Blotting your regular sunscreen on top of your makeup using a sponge applicator is the safest and most efficient option for reapplying your SPF.

Scientist and digital creator, Hannah English has an excellent tutorial for how to effectively apply sunscreen over makeup that we recommend following as it allows you to protect your skin and keep your makeup intact.

Whether it's mineral sunscreen or chemical sunscreen, it will take very little time out of your day to reapply sunscreen every 2 hours.

Making sunscreen part of your daily routine will normalise it for you and those around you too — the extra added protection from the sun will yield benefits for your skin for years to come.