How much sunscreen you really need to use for a full-body application

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Dr. Shreya Andric is a dermatologist based in Sydney. She is passionate about skin health and her mission is to educate the public on how to care for their skin, and also clear up the vast amount of misinformation out there on this topic.

While Dr. Andric has independently chosen the products that appear in this article, she does not receive revenue from the links. Some of the links may return revenue to Yahoo Lifestyle Australia.

Dr Shreya Andric is a Sydney-based dermatologist on a mission to educate people on how to look after their skin. Photo: supplied.
Dr Shreya Andric is a Sydney-based dermatologist on a mission to educate people on how to look after their skin. Photo: supplied.

How do sunscreens work?

Sunscreens work in two ways – by either scattering and/or absorbing ultraviolet (UV) radiation to help stop it from reaching the skin.

Those that scatter UV light are called physical blockers and include zinc oxide and titanium dioxide. Those that absorb UV light are called chemical blockers and include oxybenzone, octocrylene, 4-Methylbenzylidene camphor and Butyl methoxy.

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What actually is SPF?

SPF stands for sun protection factor and it relates to the amount of time it takes for redness to appear on the skin compared to when no product is used at all. This is tested in a laboratory.

For example, if it takes 10 minutes for unprotected skin to show redness, then when an SPF30 sunscreen is applied correctly, it should take 30 times longer (300 minutes) to burn. For SPF 50, it will be 50 times longer (500 minutes).

Two women wearing black and white swimsuits on a jetty at a lake. One woman applies sunscreen to the other woman's back
Yep, you should wear sunscreen every day, says dermatologist Dr Shreya Andric. Photo: Getty Images.

In real life, this is harder to achieve and factors such as skin type, UV levels, swimming/drying, and the quantity of sunscreen applied can also affect the level of protection. In theory, there isn’t a huge difference between SPF 30 and 50, however, when considering the other factors mentioned above, it is always better to start off with a higher level of protection.

Wait, I have to wear sunscreen every day?!

Sorry (not sorry), but yes! People often believe they are protected from the UV light because they are working indoors/never go outside/avoid the sun/(insert other excuse) but they forget all the incidental sun exposure that they get.

UVA is able to penetrate through clouds as well as through window glass so it is important to wear a sunscreen – at least to the face – on a daily basis.

But aren't chemical sunscreens bad for you?

The Therapeutic Goods Administration (TGA) regulates all sunscreens in Australia and has the toughest approval process in the world. They ensure that only approved ingredients, including chemicals, which have been assessed for quality and safety, are used in each product.

There have been many rigorous scientific reviews over the years and there is now a very strong list of evidence that commonly used active ingredients in sunscreen do not pose a concern for human health.

Studio isolated shot of salt in a teaspoon, includes clipping path.
Adults need a total of around 35mL (seven teaspoons) of sunscreen for a full-body application. Photo: Getty Images.

How much do I need to apply?

Sunscreen should be applied liberally and evenly to clean skin 20 minutes prior to UV exposure in order to create the intended protective barrier.

For an adult, the recommended amount is 5mL (approx. one teaspoon) for each arm, leg, body front, body back and face (including neck and ears). That is, a total of around 35mL (seven teaspoons) for a full-body application.

Do I really need to reapply?

Yes — sunscreen needs to be reapplied every 2-3 hours, irrespective of water resistance – it is water-resistant, not waterproof.

Swimming, sport, sweating, and towel drying can reduce the effectiveness of the product, so sunscreen should always be reapplied after these activities, regardless of the time since last application.

$49 at Sephora

Ultra Violette Supreme Screen SPF 50+, $49 from Sephora. Photo: Sephora.
Ultra Violette Supreme Screen SPF 50+, $49 from Sephora. Photo: Sephora.

$22.39 $31.95 at Chemist Warehouse

La Roche-Posay Anthelios Invisible Fluid Facial Sunscreen SPF 50+ 50ml
La Roche-Posay Anthelios Invisible Fluid Facial Sunscreen SPF 50+ 50ml, $22.39 from Chemist Warehouse. Photo: Chemist Warehouse.

I have SPF in my moisturiser/makeup – isn’t that enough?

Quick answer – no. Mostly because we tend not to use enough. If you’re trying to skip a step, choose a hydrating sunscreen instead so that you may not need to use a separate moisturiser.

Can I put sunscreen on my baby? Does it need to be a specific kids sunscreen?

Sunscreens are generally not recommended for use in babies under the age of six months as they have very sensitive skin which may be more likely to suffer a reaction.

Instead, try to keep babies away from direct sunlight as much as possible when UV levels are 3 or above (this is easy to find on your smartphone weather app), as their skin is more sensitive than adults.

Young Asian boy at the beach having sunscreen applied to his face
For kids from the age of two upwards, a regular sunscreen should be fine to use. Photo: Getty Images.

Try to minimise time outside during the middle of the day (between 10am and 4pm) when UV levels are at their strongest. When this is not possible, ensure babies are protected from the sun by shade, protective clothing, and a hat.

Over six months of age, a baby sunscreen is preferred as they are generally made for more sensitive skin. From the age of two upwards, a regular sunscreen should be fine to use. Exposure to UV radiation during the first 15 years of life significantly increases the risk of developing skin cancer later in life.

What's the best sunscreen to buy?

The one you will use! Given the strict TGA approval process, any sunscreen purchased in Australia will do the job so long as you use it correctly. Buy one that suits your skin type and that you're happy to apply and reapply on a daily basis.

Disclaimer: sunscreen is only one of the ways to protect yourself from the sun. You should also protect your skin with protective clothing, wearing a broad-brimmed hat, seeking shade, and wearing sunglasses.

$18.69 $31.50 at Chemist Warehouse

Cancer Council SPF 50+ Kids 500ml Pump, $18.69 from Chemist Warehouse
Cancer Council SPF 50+ Kids 500ml Pump, $18.69 from Chemist Warehouse

$20.39 $33.99 at Chemist Warehouse

Nivea Sun SPF 50+ Protect & Moisture Lotion Pump 1L, $20.39 from Chemist Warehouse
Nivea Sun SPF 50+ Protect & Moisture Lotion Pump 1L, $20.39 from Chemist Warehouse

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