Sunscreen Explained - The Big SPF Questions Answered


Over the last few weeks, the big sunscreen debate raised its head yet again after Gwyneth Paltrow appeared in a video by Vogue magazine discussing her skincare routine.

During the video she described how she uses SPF as a ‘highlighter’ and that certain sunscreen ingredients are ‘toxins’. Whilst I have great respect for Gwyneth on many levels – she is an incredible actress, an astute businesswoman and an admirable activist, her take on this is at best misinformed, and at worst, damaging.

As a public figure who commands a great deal of exposure and media clout, making these claims not only runs the risk of undoing decades of great work on the part of skin cancer awareness campaigns, but could also undermine the increasing and extensive clinical evidence base supporting the use of daily sunscreen in skin cancer prevention.

In the UK alone, there are over 100,000 new cases of skin cancers per year, the majority of them being preventable so awareness of sunscreens should be a must for all of us.

What is UV light? – and what are the differences between UVA and UVB?

UV light is a high frequency form of light that is not visible to the human eye – it’s on the electromagnetic spectrum beyond that of violet light.

The sun constantly emits UV light which reaches our skin and the light energy is converted into heat and chemical energy (in the form of oxidative free radicals). These in turn cause damage to our DNA and other structures in our skin, such as collagen, resulting in cellular changes, cancer and skin ageing.

Our skin responds to this UV light exposure by activating pigment cells, known as melanocytes, in the upper level of our skin (the epidermis). These cells produce a pigment called melanin whose function is to absorb UV light and prevent it from penetrating deeper into the skin, where it causes damage to other cells and deeper structures.

Over time, this causes a tan to develop, and over the longer term, pigmentation marks develop.

There is often a misconception that UV light is only high in the wintertime. The truth is that whenever it is daylight, UV light reaches your skin and causes damage. There are three main types of UV light, UVA, UVB and UVC, of which two reach the earth’s surface – UVC is filtered out by the atmosphere.

UVA light accounts for about 95% of all UV light reaching the surface of the earth (and your skin). It can penetrate deeply into your skin, through all the layers, even into the fat beneath the skin.

  • Reaches the deepest layers of the skin causing extensive damage to collagen and elastin, as well as indirect damage to structures in skin cells, such as DNA due to release of free radicals
  • Tends not to cause much inflammation, erythema or sunburn
  • UVA is present year-round at consistent levels (yes, even in the deepest of winters)
  • It penetrates through clouds, water and glass
  • Strongly associated with the longer-term development of melanomas and other skin cancers
  • Strongly associated with development of features of ageing in the skin including persistent pigmentation darkening and dermal thinning
  • Over time can even cause damage to the fat beneath the skin, causing volume change in the face associated with ageing
  • Causes tanning by oxidation of melanin precursors in deepest level of the skin, not by increasing melanin content

UVB light accounts for about 5% of the UV light reaching your skin. It is shorter wavelength but higher energy than UVA, meaning it only penetrates the top layers of skin but causes more intense short-term effects.

  • Reaches the epidermis and upper dermis layers of the skin (mostly filtered by melanin in the epidermis)
  • Tends to cause inflammation and sunburn
  • Causes direct DNA damage to skin cells, including melanocytes
  • Causes delayed tanning by increased production of melanin by melanocyte cells after exposure
  • UVB levels are higher in summer months and between 10am and 4pm during the day
  • Filtered by glass
  • Strongly associated with development of skin cancers

Why should I use sunscreen on a daily basis?

Skincare SPF

Throughout the scientific literature, it has been shown consistently that UV light from the sun (and artificial sources, such as sunbeds) is directly and strongly linked to development of all types of skin cancers and every hallmark of ageing in the skin, including collagen loss, pigmentation and volume change.

UV light reaches the skin and converts to both heat and chemical energy, resulting in the development of oxidative free radicals in the skin as wells as doing direct damage to the structures of the skin.

As I mentioned above, UVA light is present year-round, so protection against this is important every day. In terms of your skincare routine, it is the single most important step in anyone’s skincare routine, regardless of skin type, location or time of year.

How can I reduce UV damage to the skin?

There are a number of ways of avoiding or minimising the damaging effects of UV light:

  1. Sunscreens – for areas that are not covered by clothing, it’s important to use skincare that blocks the penetration of UV light into the skin. These work in different ways (which I’ll cover later) to stop UV light reaching the cells and deeper structures of the skin.
  2. Avoid direct exposure – stay out of the sun wherever possible, particularly mid-day to late afternoon, when UVB levels are highest in the summer.
  3. Cover up – if you are out in the sun then wearing clothing is a sure way of protecting certain areas of the body during daylight hours. Many fabrics are now available with built in UV protection so keep an eye out for these when selecting your next clothing purchase.
  4. Antioxidant support – as I mentioned, UV light results in damage through the production of free radicals in the skin (also known as Reactive Oxidative Species (ROS)), which are high energy molecules that cause chemical damage to the structures they are in contact with, such as DNA and collagen. This in turn results in DNA changes and inflammation, causing a sequence of destructive reactions in the body. These molecules can be neutralised by antioxidants such as vitamin E (tocopherol) and vitamin C (ascorbic acid) from skincare and from within the body. These molecules can be found in many skincare products, including serums and moisturisers. Whilst these should not be used as a substitute for sunscreens, having good levels of antioxidants in your skin does offer a degree of protection against future UV damage due to free radicals.

What does the rating on sunscreens mean?

You will likely have heard of the SPF rating system for sunscreens. This is a standardised way of describing how much UVB light a particular product filters out at the recommended dose. It relates only to UVB, not to UVA, for example:

  • SPF 15 filters out 92% UVB light
  • SPF 30 filters out 97% UVB light
  • SPF 50 filters out 98% UVB light

Most sunscreens will also filter a percentage of UVA light so would be described as ‘broad spectrum’ on the packaging. There are two ratings of UVA filters – the star system (from 1-5 stars) and the PA system. In the EU, it is recommended that for any sunscreen product the level of UVA protection should be at least a third of the SPF protection (i.e. 1/3 of the level of UVB protection) – if a product has achieved this it can use the symbol UVA in a circle on its packaging.

Any sunscreen you select should be photostable, meaning that it does not break down on exposure to light, and also water resistant and rub-resistant. This will usually be noted on the packaging.

What’s the difference between chemical and mineral sunscreens?

Black and white image close up of skin

There are two major forms of UV filters used in sunscreens, each with individual benefits and drawbacks. When choosing a sunscreen, the most important consideration should be the level of protection it gives, rather than the form of filters used. The two forms are:

Mineral or Inorganic (‘reflectors’)

  • These are metal oxides that sit on the skin surface and reflect UV light
  • The most commonly used are Titanium Dioxide and Zinc Oxide
  • Mineral screens tend to be inert chemicals that are generally believed to not be absorbed by the body
  • They tend to form a chalky film when exposed to water or sweat
  • Inorganic screens tend to be less water resistant than organic screens.

‘Chemical’ or Organic (‘absorbers’)

  • These include a range of carbon-based molecules that absorb UV rays and convert them to infrared to prevent them penetrating into the skin
  • A wide number of molecules have this property, however, some are not available in the US
  • These tend to be more water resistant than inorganic filters
  • There has been some controversy around chemical screens as it is believed that some may be absorbed into the body, with one type of screen (oxybenzone) being shown to have oestrogenic effects. This has now been banned for use in the USA and is now rarely used.

How much sunscreen do I need to use?

The British Association of Dermatologists’ recommendation is that sunscreens will each have their own recommended guidance on the packaging, however, the type of filter (organic/inorganic), activity during the day and water resistance of the product will have an effect on the level of protection at any given time and the amount required to give the stated level of protection.
Generally speaking, the convention is that sunscreens should be applied 15-30 minutes before going out in the sun then reapplied every 2 hours. After swimming or exercise, particularly after towel drying (which removes an estimated 85% of any product), sunscreen should be fully reapplied.
Organic (‘chemical’) filters tend to allow for a thinner film to be used so are lighter weight and clear, whereas inorganic (‘mineral’) filters may result in a more whitish film being created until they rubbed in fully.
When testing sunscreens, regardless of the product, most clinical testing will be done using 2mg/cm2 of any product – meaning that to cover the face and neck (including the ears) at least half a teaspoon will be needed to give the level of protection stated.
It is important also to note that certain materials, such as snow and sand reflect UV light so can increase the power of UV radiation – so using a higher level of protection and more frequent reapplication is recommended.

Is SPF in my moisturiser enough?

Any product containing SPF will be subject to the same level and conditions of testing, so a moisturiser containing SPF will be tested in the same way that a sun cream or lotion is. It is important to check that any moisturiser with SPF you use contains a filter that is water- and rub-resistant and that it contains a UVA filter (i.e. it is ‘broad spectrum’).
With my Dr. David Jack All Day Long moisturiser, I selected an organic lightweight filter that provides an advanced lightweight water/rub resistant SPF 50 with broad spectrum filters – it blocks both UVA and UVB. Since it is SPF50, it should provide protection against 98% of UVB rays and will block UVA also.

What about vitamin D?

You may be aware that vitamin D is created by the body in the skin from cholesterol, and relies on UVB radiation to convert this cholesterol into the active form of vitamin D in the skin.
Vitamin D is required for many reasons for general health, including bone health, immune function and hormone functions. It may be difficult to get enough vitamin D from the diet alone, particularly in colder climates with less sun, especially in those with darker skin types.
With this in mind, the British Association of Dermatologists has advised that although sun should not be avoided entirely, it cannot advise on how much sun exposure is needed for the normal production, and that ideally vitamin D should be derived as much as possible from diet and supplements to meet the daily recommended requirement of 10mg/day (400IU/day).
With this in mind, I added 5mg (200IU) of Vitamin D3 per serving to my SkInfusion supplement, to ensure that you can top up your dietary intake of vitamin D easily to the recommended level.
For more information on sunscreens, vitamin D and skin cancers, please visit the website of the British Association of Dermatologists, where you can find extensive advice and guidance on all things skin!

Useful Resources

British Association of Dermatologists