Balsam Alabassi and Lorna Bowes explain how sunscreen works to protect skin from UV radiation
Consumers are becoming increasingly aware of the differences between UVA and UVB radiation and the varying effects that environmental factors such as UV and pollution have on the skin. Aesthetic practitioners need to ensure that they are giving their patients the right information and advice on sun and skin protection. When discussing sun protection as it relates to aesthetic practice, there are a number of different topics that need to be covered: what is ultraviolet radiation and what effect does it have on the skin; what skin conditions can be exacerbated by exposure to UV rays (a subject not covered in this article); what ingredients can provide adequate protection from the sun; ingredients that are also photoprotective; and what amount of sunscreen should be applied and how frequently.
UV radiation – what is it?Ultraviolet (UV) radiation is categorised by wavelength as UVA, UVB and UVC. UVC radiation (wavelength 320-400) is absorbed by the ozone layer and has no effect on the skin,1 so this article is concerned only with UVA and UVB rays.
Even on a cloudy day, more than 80% of UV radiation makes it through the clouds, and exposure can be increased by other factors – both sand and snow reflect the rays, causing an increase in UV exposure of 20% and 80% respectively.1
What does UV radiation do to the skin?UV radiation is an oxidative process that stimulates the production of free radicals (unstable oxygen molecules that have lost one of their two electrons), which cause cellular damage. It has both immediate and long-term effects on the skin.2 Some of the immediate effects of the sun on the skin are DNA damage, immunosuppression and sunburn. Sunburn is caused by UVB radiation2 and is a physiological reaction to over-exposure to the sun. This process, known as apoptosis, is a form of cell suicide, where the keratinocytes – the cells that form a barrier to protect the skin from environmental damage – are broken down in an attempt to minimise the risk of skin cancer.3 Both UVA and UVB rays can cause long-term damage to the skin, although UVA is the root cause of accelerated ageing, as UVA rays can penetrate the dermis and be absorbed by fibroblasts and stimulate matrix metalloproteinases (MMPs).4 This reduces fibrillin and collagens I, III and VII, and increases elastotic material, all of which contribute to the visible effects of ageing: lines, wrinkles, volume loss and skin laxity.2 Long- term exposure to UV radiation is also associated with an increased risk of skin cancer – most commonly squamous cell carcinoma and basal cell carcinoma – due to the creation of free radicals.2
Ingredients to look forBroadly speaking, sunscreen ingredients can be divided into physical and chemical sun blocks. The most common physical blocks are zinc oxide, titanium dioxide and iron oxide, all of which physically block the sun’s rays from entering the skin.5 Chemical sunscreens, however, such as phenylbenzimadole sulfonic acid, avobenzone and octyl methoxycinnamate, work by absorbing the UV radiation themselves.6 Both physical and chemical sunscreens have their disadvantages; historically it has been almost impossible to find a physical block that doesn’t leave a tint on the skin, which can be frustrating for those with darker skin. New techniques are allowing products to be formulated with far smaller particles of physical filters such as titanium dioxide and zinc oxide.7 As such lightweight, photostable, virtually transparent, fluid, broad spectrum, mineral sun protection at SPF50 is a reality. Chemical sunscreens, whilst previously preferable on an aesthetic basis, can cause dermatitis or photocontact allergy.8
AntioxidantsAntioxidants can fight the effect of free radicals, and it has been proven that a combination of both oral and topical antioxidants provides antioxidative activity in different structures, and can inhibit the effects of UV radiation and prevent skin damage.9,10 Potent antioxidants include vitamins C and E, and more recently polypodium leucotomos, a tropical fern extract known to have significant antioxidant properties.9 One specific effect of UV exposure is lipid peroxidation in cell membranes and mitochondria leading to cell damage.11 In addition, the ingredient maltobionic acid has been shown to reduce the production of malondialdheyhde, an oxidative degradation product, as well as inhibit UV- induced lipid peroxidation.12 Lactobionic, another bionic polyhydroxyacid, is a powerful metal chelator, and additionally has been shown to improve barrier function12 and prevent inflammation.13
A further study reviewed lactobionic acid looking specifically at capacity for MMP inhibition and lipid peroxidation. The study demonstrated strong in vitro MMP inhibition as well as the capacity to block collagen degradation, helping to preserve the skin matrix in photoaged and naturally ageing skin.14 The polyhydroxyacid, gluconolactone is a cell nutrient and antioxidant15 that also exhibits MMP inhibition, increased viable epidermal thickness and increased glycosaminoglycans.16
Reducing unwanted pigmentationThere are many ingredients shown to reduce hyperpigmentation, of those already discussed above, maltobionic acid inhibits MSH-stimulated melanogenesis and so as well as being a powerful antioxidant, it is also a pigment-evening agent.17 Likewise, lactobionic acid has been shown to effectively inhibit UV-triggered melanin synthesis helping to prevent hyperpigmentation in sun-exposed skin.18
The vitamin D debate
Vitamin D deficiency is becoming an increasing problem, as we become more aware of the risks of exposure to the sun. In a 2008 study, Holick showed that sunlight is the main source of vitamin D for humans, as it is very difficult to derive adequate vitamin D from food, and we rely on UVB photons to synthesise vitamin D3.22 Sadly, the use of sunscreens does have a negative impact on vitamin D3 synthesis, and it is important to be aware of the importance of vitamin D when advising patients on sun protection. Vitamin D deficiency is associated with rickets, growth retardation and osteoporosis, as well as increasing the risk of certain cancers and autoimmune diseases.2 To avoid this, it may be advisable to recommend that patients take a daily supplement of vitamin D.
How can we advise patients on sun protection?In general, patients can work out how frequently they need to reapply their chosen sunscreen by multiplying the SPF by the length of time it takes for their skin to burn without sunscreen – for example, if they usually burn in ten minutes and they are using a product with an SPF of 10, their skin will be protected for 100 minutes, after which they will need to apply more sunscreen.19 If your patient has been undergoing treatment that is likely to affect the natural barrier provided by the skin – a chemical peel or laser treatment, for example – then it is essential to recommend a higher, broad-spectrum SPF.
Why broad spectrum?SPF 15 protects against more than 93% of UVB rays, and there is only a slight increase in that protection to 97% with an SPF of 30+, and 98% for SPF 50+.20 In fact, the level of SPF is less important than the amount of product applied and exposure to water or sweat. NICE guidelines now state that provided it is applied properly, SPF 15+ is sufficient to protect the skin from the sun, however, a higher, broad spectrum SPF is recommended by most dermatologists.21 Unless the sunscreen used is broad spectrum, covering a wide range of wavelengths, it will only provide protection against UVB radiation. Whilst this will prevent burning, and offer some protection against skin cancer, it will not affect UVA radiation, which is the main culprit when it comes to accelerated ageing and other skin concerns.20 It is also important to note that no sun protection product is truly waterproof – products are now described only as ‘water resistant’ and should be reapplied after contact with water – and that use-by-dates are as important for sunscreens as for any other product. If a sunscreen has exceeded its expiry date, it may well be ineffective.
ConclusionA broad-spectrum sunscreen, with an absolute minimum SPF of 15+ should be used daily, throughout the year, regardless of the weather for exposed skin. However, as an aesthetic practitioner, it is vital that you take into account any procedures your patient has undergone that may necessitate a higher SPF, and that you advise on the manner of application – a minimum of 30ml should be used to cover the whole body, and this should be reapplied at least every two hours, more often if the patient comes into contact with water, unless the product is one of a new breed of ‘all-day-wear’ sun protection.
Ensure that your patient is aware of the importance of checking the expiry date on their sunscreen, and suggest the use of oral and topical antioxidants, as well as ingredients to support barrier functions and reduce the risk of pigmentary disorders, alongside or even within sun product application to maximise skin protection. Aesthetic practitioners can and should play a vital role in helping patients to protect their skin from the sun, as this can have a dramatic effect on the need for future treatments, as well as preventing cancer and other sun-induced skin conditions such as photodamage and associated aesthetic changes.