The Australian summertime drill seems simple enough: slip on a shirt, slop on some sunscreen and slap on a hat.

But if you have ever found yourself staring back at a regretful, hyper-sensitive, pink-skinned version of yourself in the mirror thinking "that sunscreen didn't work as well as it should have", then you're probably doing sunscreen wrong.

Australia has one of the highest rates of skin cancer in the world, and the importance of protecting your skin cannot be overestimated.

Here are some tips on how to do sunscreen right — and avoid rocking up to work, after a weekend in the sun, looking like lobster (we've all been there).

How much sunscreen should I apply?

According to health experts, you should aim for one teaspoon of sunscreen per limb, one each for the front and back of the torso, and one for the face, neck and ears. That's a total of seven teaspoons (if you intend to be outside with just your bathers on).

Since very few of us take an actual teaspoon to the beach, seven teaspoons is roughly "a cupped handful", says sunscreen tester John Staton.

The Cancer Council recommends using SPF30 (or higher) broad-spectrum, water-resistant sunscreen.

You should apply sunscreen at least 20 minutes before going outdoors and re-apply every two hours.

"Until you fill the skin so you've got a continuous film, you're not anywhere near fully protected. Once you've done that, the amount you put on top of that is going to give you the extra protection," Mr Staton says.

Chemical vs physical sunscreen

There are two types of sunscreen: chemical and physical (although, as Mr Staton points out, scientifically they are all chemicals).

Chemical sunscreens work by absorbing UV radiation. They take about 20 minutes to sink in, and are resistant to sweat and water (unlike physical sunscreens) — so they're a good option if you're going swimming or playing sport.

Physical sunscreens contain minerals (zinc oxide or titanium dioxide) and work to reflect and scatter UV radiation, providing you with a literal shield against the sun.

Not so long ago, physical sunscreens looked like an actual shield — remember the zinc on the noses of test cricketers?

These days, physical sunscreens contain nano-sized titanium dioxide particles and zinc oxide particles, which means you can block the UV without the white stripes.

There have been concerns about the use of "nanoparticles" (really really tiny particles, their size is measured in nanometres, one nanometre being a millionth of a millimetre) and whether they can penetrate the skin and have a toxic effect.

A 2013 review by the Therapeutic Goods Administration (TGA), which regulates sunscreens sold in Australia, concluded that studies had shown nano-sized titanium dioxide and zinc oxide particles do not penetrate the underlying layers of skin, and that "on current evidence neither … are likely to cause harm when used as ingredients in sunscreens".

And the research hasn't stopped. The Cancer Council Australia (CCA) agrees with the assessment that on available evidence, nanoparticles do not pose a risk, but says it will continue to monitor new studies.

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Help! I've got sensitive skin

Sunscreens are complex formulations that can easily irritate the skin — and sometimes cause allergic reactions.

As a general rule, most sunscreens on the supermarket shelf have chemical filters, unless they state otherwise. If you've got sensitive skin, it's best to look for something with a specific physical, mineral or 'sensitive' label.

You should also be mindful of artificial fragrances — one of the most common skin-irritants found in sunscreen. If have a reaction to a sunscreen, try a fragrance-free product.

What's the deal with SPF?

The sun protection factor (SPF) of a sunscreen refers to the length of time it takes for your skin to burn when you are in the sun while wearing sunscreen.

Research, however, shows people typically use only 25 to 75 per cent of the amount used by testers in the process that determines the SPF number on the bottle.

Since the protection factor varies with the amount of sunscreen applied, that means most users probably achieve a level of protection 20 to 50 per cent of that expected from the SPF on the label.

A higher SPF is no better unless it's applied correctly, so it's important to cover yourself with ample sunscreen, apply it early, ensure you don't miss any spots, and remember to reapply.

When should I apply sunscreen?

Sunscreen should be applied during 'daily sun protection times' — when the sun's ultraviolet (UV) radiation reaches damaging levels of three and above.

UV radiation levels in northern parts of Australia are generally higher than in the south, so in some parts of the country, sun protection is needed all year round.

Unlike light or heat from the sun, UV radiation cannot be seen or felt, and we often don't know that it's damaged our skin until it's too late.

The UV can be high even on cool or overcast days, so never rely on clear skies or high temperatures to work out whether you need to slip, slop, slap.

Daily forecasts for when the UV Index is set to reach three or above can be found on the SunSmart app or via the Bureau of Meteorology.

During sun protection times: Slip on sun protective clothing

Slip on sun protective clothing Slop on SPF30 (or higher) broad-spectrum, water-resistant sunscreen

Slop on SPF30 (or higher) broad-spectrum, water-resistant sunscreen Slap on a broad-brimmed hat

Slap on a broad-brimmed hat Seek shade

Seek shade Slide on sunglasses

But I'm naturally tanned…

There is no such thing as a safe or healthy tan. In fact, a tan is a sign that your skin has been damaged by UV radiation.

Both a tan and burn are signs of damage from the sun's UV radiation ( Getty Images: Nisian Hughes )

According to SunSmart: "Although many think of tanning as attractive, it's actually a result of your skin cells producing a pigment called melanin, in an effort to defend your skin against the UV damage that has already occurred."

A tan offers very limited protection from sunburn. Most importantly, a tan does not protect you from DNA damage, which can lead to skin cancer.

But I need my daily Vitamin D fix…

While sun exposure is important for good health, the harms of UV radiation in Australia far outweigh the risks of vitamin D deficiency.

For most people, adequate vitamin D levels can be reached through regular incidental exposure to the sun.

During summer, when the UV reaches damaging levels of 3 and above, a few minutes of sun exposure on either side of the peak UV periods (before 10:00am and after 3:00pm) is enough to get your vitamin D fix.

But Pete Evans says sunscreen is full of poisonous chemicals…

Don't listen to Pete Evans.

But sunscreen alone isn't enough…

You're right! No sunscreen provides full protection from the sun, so never rely on sunscreen alone.

Combine it with sun-protective clothing, a broad-brimmed hat, sunglasses, and a spot in the shade.