Lab notes
Sunscreen: 6 of your top questions answered

Sunscreen: 6 of your top questions answered

This week we deep dive into some of the most commonly asked questions about sunscreen

It’s been freakishly sunny in the UK over the last few months (the irony has not been lost on us that the majority of us were essentially trapped indoors on what was apparently the hottest spring in 127 years.) But indoors or outdoors, on sunny days or rainy ones, one thing we know: sunscreen is your skin’s best friend. But how much do you know about this miracle worker? Here we answer 6 common questions on our beloved sunscreen

1.Do I need sunscreen on a cloudy day, or if I’m not going outside during 11-3?

Yes. Absolutely. 100%. 80% of UVA & UVB rays can pass through clouds, so any time spent outside will expose the skin to UV rays. UVA rays are the longest wavelength within the ultraviolet spectrum, which allows 75% to actually penetrate glass, so even if you’re inside you should be protecting your skin daily. 

2.What does SPF actually mean?

SPF stands for ‘Sun Protection Factor’ and is quite literally the measure of how much longer it will take for the skin to burn on exposure to UVB radiation, vs. not using it. For example, if you would normally sunburn, say, within 10 minutes of direct sun exposure, an SPF15 would mean that it will take 150 minutes (2.5H) to sunburn based on the same sun exposure. 

There are some problems with this calculation, in that:

  1. Product tends to move around, especially if you’re sweating, wearing clothes, swimming etc, so real life will never quite match test conditions. 
  2. It only relates to UVB (the rays that cause sunburn), and doesn’t take into account the UVA part of the spectrum. One of the most common UVA filters used in chemical sunscreens, Avobenzone, degrades on exposure to sunlight, while protecting the skin, so there won’t be any of this filter left after 2 hours to protect from UVA rays. EU guidelines are to re-apply every 2 hours, or after swimming, sweating or rubbing the skin, whatever the SPF level. 

3. Is ‘SPF’ the full story?

SPF is a measure of UVB rays only, as it’s this wavelength of light which leads to sunburn (erythema), and was originally considered to be the whole picture. Then research evolved, we realised that UVA, which has a longer wavelength, can also cause lead to sun damaged skin, and contributes significantly to premature ageing of the skin. 

In Europe, the UVA protection must be at least ⅓ that of the declared SPF to be able to be sold as a sunscreen product. The star rating (originally coined by Boots) is a separate measure for UVA protection, with 1* being the minimum 20-40% protection, and a 5* being 90% UVA:UVB protection, so look out for this indicator or ask brands for this information - it has to be measured during the product development phase (via a ‘critical wavelength’ test), so the data will be available (although not a legal requirement to provide it). 

Newer research also shows lower energy wavelength lights such as infra-red, high energy visible, and blue light also have a damaging effect on the skin and certain brands (Heliocare 360 range and Ultrasun being 2 of our favourites) are adding ingredients into their formulations to offer extra protect against these wavelengths. 

For full disclosure, the sun also emits UVC rays, which are the highest energy wavelength and would cause a lot of damage to the body, but this wavelength reacts with the ozone layer way above the earth, and so the rays don’t reach us on the ground. 

4. What are the different types of sunscreen?

There are two types of sun filter: physical and chemical. There are just 2 physical filters, zinc oxide and titanium dioxide, which are both white mineral powders, and are also referred to as mineral sunscreens. They work by essentially creating a super fine layer over the skin, which reflects UV light, preventing it from penetrating into the skin and causing any cellular damage. This makes it a broad-spectrum filter as it essentially reflects all light. The downside to it is that it’s not a great option for those with medium-deep skin tones, as they tend to leave a white cast on the skin. Texture-wise, they’re trickier to get right and traditional formulas were thick and greasy, but technology has evolved and there are some pretty light, imperceptible products on the market now. We also wouldn’t advise a mineral sunscreen if you’re planning any flash photography as it will reflect this light too. 

Chemical filters are a bit more complicated, as they need to be used in combination in order to block the full spectrum of wavelengths associated with UVB & UVA. These filters work by absorbing into the skin, and then converting UV energy into heat, dissipating the energy which could cause harm in the body. Certain chemical filters are more likely to irritate the skin vs mineral options, which are usually a great option for sensitive skin. 

5. How much sunscreen should you use?

Official guidance on how much to apply is for ½ teaspoon to cover face, neck & ears. 2 tablespoons would cover your whole body (assume you’re in a swimming costume). 

6. How long does sunscreen last?

Sunscreen is definitely one product you don’t want to use past the PAO (‘period after opening’ - the little open jar you’ll find on the back of pack which tells you how long the product is stable/compatible in that packaging once opened). As the filters can degrade over time, particularly at higher temperatures (bathrooms/near windows/on the beach etc), I would definitely not recommend using a sunscreen past this date. 

Maybe you knew a lot of that already, or maybe we’ve blown your mind? Either way, sunscreen is one of the hardest products to get right, so if you’re still wondering what type of sunscreen is best for you, you can receive personalised recommendations by starting your free online consultation here