Sun protection factor, or SPF, is a measure of how effectively a sunscreen product can protect your skin from the harmful effects of the sun’s ultraviolet (UV) radiation.1 Photoprotection is one of the leading preventative health strategies people can work with in the world of skincare and aesthetics.
Routine use of SPF has been shown to reduce melanoma risk, as well as the incidence of actinic keratoses, solar elastosis and squamous cell carcinoma.2-4 It is crucial that aesthetic practitioners understand the science behind SPF so they can properly advise their patients on the necessity of its use.
SPF over the years
Even though SPF is a relatively recent innovation, protecting the skin from the sun is not new. In ancient Egypt, pale skin was highly prized, and skin was protected with rice bran, jasmine and lupine. All three of these ingredients are now reported to have protective effects: rice bran absorbs UV light, jasmine repairs DNA and lupine has been shown to lighten skin.5
In ancient Greece, olive oil was the suncare ingredient of choice, and has recently been shown to have an SPF of eight.5,6 Umbrellas, veils and wide-brimmed hats can be seen in paintings from ancient civilisations across the globe. Study of art shows us that lighter skin was more desirable for centuries, and both men and women are depicted wearing hats, visards (full-face masks for protecting the skin while travelling) and whitening products containing lead.7
In 1801, the German chemist, physicist and philosopher Johann Wilhelm Ritter is reported to have discovered UV radiation; at the time, he named it ‘chemical rays’.8 In 1820, Sir Everard Home, the first president of the Royal College of Surgeons, reported on the effects of sunlight on exposed skin versus skin covered by a black dense material, demonstrating that it was something other than heat causing skin damage.9
In 1870, Austrian scientist Otto Veil described the effects of tannins as methods of sun protection. Given the social desire for pale skin, the obvious darkening effects of the tannins prevented them from becoming commercially viable.9 In the following decades, many papers were published reporting on the links between UV radiation, erythema and burns, and between sun exposure and skin cancer.9,10
Concurrently, work was being published on the use of chemical sunscreens for prevention of erythema solare caused by UV radiation.9 The German physician Dr Paul Unna developed a sunscreen using aesculin from chestnut extract in 1910, but the formulations were cosmetically inelegant and widely unliked.9
It was then not until 1935 that French pharmacist and founder of L’Oréal Eugene Schueller created products with UV filters. Benzyl salicylate was the active ingredient, with its reported sunny smell, and the product Ambre Solaire was born.9 Although for a time the ingredient was removed in favour of more effective sunscreens, its distinctive aroma meant it was partially reintroduced purely for its reputation as an emblematic scent of summer.11
Over the next decades, various ingredients came and went, including 2-naphthol-6 and 8-disulfonic acid salts, tannic acid, para-aminobenzoic acid derivatives, 2-phenylimidazole derivatives, anthranilic acid, cinnamates, chloroquine and benzophenones.9 Some well-known brands arose during this time, such as Coppertone, which was developed by pharmacist Benjamin Green after he added cocoa butter and coconut oil to the red veterinary petroleum he used to protect himself from the sun while flying as a WWII airman.9
Moreover, Hawaiian Tropic was the brainchild of high school chemistry teacher Ron Rice who mixed coconut oil with zinc oxide, alkyl benzoate and isopropyl palmitate in his garage in the late 1960s.9
SPF as we know it
The SPF ratings as we know them were introduced by chemist Franz Greiter in 1962.17 Since then, SPF and its usage has evolved greatly, in line with increasing consumer demands for more sun protection. SPF is typically represented as a numerical value, such as SPF 15 or SPF 30. This value is calculated based on a concept called the ‘minimal erythema dose’ (MED) which is the minimum dose of UV radiation to induce redness.18
SPF values represent the ratio of MED on protected skin to MED on unprotected skin.18 This indicates how much longer it will take for your skin to become sunburnt while wearing the sunscreen, compared to not wearing any at all. For example, if it takes 10 minutes for your unprotected skin to start turning red in the sun, a sunscreen with an SPF of 30 would theoretically provide protection for 300 minutes (30 times longer) before your skin starts to burn.19
In the UK and EU, the maximum SPF rating allowed is 50+ so consumers aren’t lulled into a false sense of security that their sun protection is infallible.20
It’s important to note that SPF only measures protection against UVB rays, which are the primary cause of skin inflammation (sunburn) and pigmentation (suntan).21 It doesn’t measure protection against UVA rays, which are less carcinogenic than UVB rays and cause oxidative damage via free radicals.21 To ensure maximum protection, it’s recommended to use a sunscreen that offers broad-spectrum protection against both UVA and UVB radiation, and reapply it every two hours or after swimming or sweating.19
The UK and EU regulations permit a range of ingredients to be used in sunscreens. These include organic (chemical) UV filters that absorb UV light and release it as heat, such as avobenzone, octocrylene, octisalate, homosalate and octinoxate. As these ingredients can absorb into the skin, they can cause irritation.22 Although they are well suited for easy application, they do need to be reapplied frequently.22
In addition, there are inorganic (physical or mineral) UV filters which absorb, scatter or deflect UV, as well as absorbing UV light and releasing it as heat. They are able to offer protection as soon as they are applied, but are prone to being removed by sweat and water. Ingredients such as titanium dioxide and zinc oxide are commonly used, but can leave a whiteish hue which can be especially visible on darker skin tones, leaving formulators with the challenge of negating this.22 Some new physical/inorganic sunscreens are using nanotechnology whereby active ingredients are contained in nanoparticles which are not easily seen.
Sunscreen products in the UK typically use a combination of several active ingredients to provide sun protection, with varying functions.23 Different sunscreens may contain different combinations and concentrations of both SPF ingredients and other active ingredients, as well as inactive ingredients such as preservatives, fragrances and emollients. Common examples of these ingredients are outlined below.23
Avobenzone
Avobenzone is an oil soluble chemical filter which works by absorbing a wide range of UV rays as they enter the skin, before converting them into energy that is less damaging for cells. To ensure it remains effective, this ingredient needs to be combined with other UV filters as it can breakdown during prolonged exposure to sunlight.23
Octinoxate
A potent UVB absorber, chemical filter octinoxate is a cinnamate ester. As with other chemical filters, it tends to be used in combination with other chemical or physical filters.23
Octisalate
Octisalate absorbs UVB rays as they enter the skin, and is often combined with avobenzone and other chemical filter ingredients.23
Homosalate
Homosalate is a chemical filter which absorbs UVB rays that penetrate the skin, converting them into heat and reducing cellular damage.23
Oxybenzone
Oxybenzone filters both UVB and UVA rays. Most UV filters are improved when used in combination, and oxybenzone can also help prevent the deterioration of other UV filters in the same formula. However, research demonstrating potential damage to reefs and fish means that organic filters using this ingredient are banned in many regions such as Hawaii.23,24
Zinc oxide
A physical (or inorganic/mineral) sunscreen, zinc oxide effectively defends the skin against both UVA and UVB rays by creating a protective barrier over the surface of the skin to provide instant protection. Zinc oxide is gentle on the skin and long lasting, but can leave a white cast; however, this can be negated when used in a nanoparticles formulation.23
Titanium oxide
A broad-spectrum physical (or inorganic/mineral) UV filter that blocks and scatters UV rays.23
Application of sunscreen
Given the amount of time people choose to spend in the sun for leisure, and/or are required to be exposed to UV at work, understanding how and when to apply SPF is crucial so you can advise your patients.
According to the British Association of Dermatologists (BAD), we still go out of our way to tan, with a third of 2,163 UK adults (33%) reporting that they deliberately tried to develop a tan through sun exposure in 2022, either through deliberate sunbathing (21%) or spending time in the sun without sun protection (12%).26 Sunbathing was most popular amongst women, with a quarter (25%) saying they sunbathed with the intention of developing a tan.26
Sunscreens must be applied at a thickness of 2mg/cm2 to achieve the labelled SPF. Studies have shown that only 20-50% of this amount is actually applied.27 Advice from the Canadian Cancer Society and the American Academy of Dermatology has been widely adopted (Figure 1).
The following are the BAD tips for applying sunscreen:26
- Apply sunscreen liberally to exposed sites 15-30 minutes before going out into the sun
- Don’t rub the sunscreen into your skin but spread the sunscreen as uniformly as possible over the surface of the skin and allow to dry
- Re-apply sunscreen to exposed sites 15-30 minutes after sun exposure begins
- Re-apply sunscreen after vigorous activity that could remove sunscreen, such as swimming, towelling or excessive sweating
- To maximise quality, sunscreens should be stored in a cool, dry place, out of direct sunlight
- Always refer to the ‘period after opening’ symbol on the labelling, as products have a fixed life after they have been opened
Crucially, patients should be reminded that SPF should be applied and reapplied all year round, not just in the warmer months, as UV rays can affect the skin whether the sun is shining or not. UVB peaks during summer months in the UK and is stopped by clouds and glass, while UVA is present throughout the year and can penetrate clouds and glass.10
Non-SPF approaches to photodamage management
There are an increasing number of ingredients reported to have effects on preventing or managing the sequelae of photodamage. They should be used alongside, rather than as an alternative to, SPF products. These include:
Antioxidants: Multiple antioxidants including vitamins A, C and E, glutathione, niacinamide, epigallocatechin gallate (EGCG), curcumin (diferuloylmethane) and can be effective in supressing UV-induced sun damage.12
Retinoids: Retinoids describe all forms of vitamin A, both natural and synthetically produced derivatives. Topical retinoids are widely recognised in the management of hyperpigmentation and photoageing, as well as reducing fine lines and wrinkles.13
Hydroxy acids: Hydroxy acids break the desmosomal attachments between corneocytes, as well as reducing corneocyte cohesion. This triggers a 25% increase in dermal thickness, increased GAGs, enhanced collagen density and improved elastic fibre behaviour.14,15
Amino sugars: Ingredients such as N-Acetylglucosamine and N-Acetyl- L-tyrosinamide have been shown to produce significant increases in production of hyaluronic acid, as well as increasingly viable epidermal thickness and dermal volume through stimulation of collagen production.16
Prioritise protection
As awareness of sun protection keeps increasing, so does demand, and we can see an increase in the number of multi-benefit SPF products coming to the market.
As well as the active ingredients and nanotechnology already mentioned, certain emerging products claim to be effective against infrared radiation and visible light, especially high energy visible light within the 400-450 nm region, known as blue light.28
It is yet to be seen to what extent various novel SPF formulations could be beneficial in other elements, but it is certainly an area set to continue growing.
As aesthetic practitioners, we know how essential skin health is for the efficacy of aesthetic treatments. Make sure to emphasise to your patients that they will get the best overall results if they look after their skin in the sun first. Most importantly, responsible use of SPF can reduce the risk of skin disease and skin cancer, so its cruciality must be recognised.
