What are the importance of sunscreens?
In the past century, we’ve spent more time outdoors with decreased clothing and with an ever diminishing ozone layer, this increases our ultraviolet (UV) radiation exposure. Especially in a country such as Australia, where we have a high rate of melanoma, it is increasingly important to protect our skin from the effects of UV radiation. UV exposure can also accelerate the rate of skin ageing, leading to premature wrinkling, loss of skin elasticity, pigmentation problems, and broken capillaries. Furthermore, these effects can occur with UV exposure that is less than levels required to cause sunburn.
What is the difference between UVA, UVB, and UVC?
UV radiation is a part of the invisible light spectrum from 280 nanometres (nm) to 400nm. UV radiation is not sensed by the skin, hence it is common to not know that you have been burnt until well after the period of sun exposure.
The UV spectrum that is relevant in causing skin damage is the UVB (290-320nm) and the UVA (320-400nm) wavelengths. UVC (100 – 290nm) is almost completely absorbed by the ozone layer and does not tend to have much effect on the skin as a result. Shorter wavelengths, such as those of UVC radiation, do not tend to penetrate the skin as deeply as longer wavelengths.
UVB radiation is responsible for classic sunburn. UVB radiation can mutate the p53 tumour suppressor gene which initiates the production of pyrimidine dimers. Elevated levels of pyrimidine dimers are linked to skin cancers. Multiple high UVB exposures in early life have been linked to basal cell carcinoma and melanoma.
UVA radiation is a more silent threat than the ‘sunburn causing’ UVB. As UVA radiation does not cause the typical redness seen with UVB radiation, it gives you no indication to cover-up or remove yourself from the sun. UVA is filtered less by the ozone layer than UVB and therefore terrestrial surface sunlight contains 20 times more UVA than UVB. UVA can also penetrate window glass and is relatively unchanged by the time of day, season, and altitude. The deeper penetration of UVA into the skin (because of its longer wavelength) also contributes to its ageing effects on the skin, including the development of excessive pigmentation, wrinkles and loss of skin elasticity. UVA radiation also plays a significant part in the development of malignant melanoma.
What is the SPF of a sunscreen?
The sun protection factor or SPF of a sunscreen is an internationally standardised measure of the ability of a sunscreen to filter UV radiation.
It is calculated by the minimum energy required to produce erythema (redness) on protected skin divided by the minimum energy required to produce erythema on skin unprotected skin. The testing for SPF occurs in a laboratory with a UV light source of measured intensity applied to 20-25 subjects who have sunscreen applied at a thickness of 2mg/cm2. Studies however, suggest that actual usage is only 25-50% of the amount used to achieve the thickness used in SPF testing.
The ‘teaspoon rule’ suggests that an adult should apply approximately half a teaspoon to each arm, and to the face and neck. 6mL (slightly more than one teaspooon) should be applied to each leg, the chest, and the back. This would make a total of 33mL for an average adult – a similar volume to that of a shot glass. The other method used is to employ a two layer technique of sunscreen application to help avoid missed areas and increase the total amount placed on the skin.
The limitations to using SPF as a guideline to UV protection include:
- The thickness of the application used to measure SPF may be unrealistic under ordinary, non-test conditions, giving the consumer false confidence whilst significantly lowering the SPF
- UVA radiation does not cause redness, and hence the SPF value may only be a measure of protection against UVB and not UVA. There is concern that those who use high SPF sunscreens (who might have otherwise limited their UV exposure due to a fear of sunburn) may remain outdoors longer and accumulate more UVA damage.
- The efficacy of a sunscreen is affected by environmental factors such as humidity and activity
- SPF is also affected by water/sweat and water resistance is defined as a maintenance of the label SPF for 40 minutes of water immersion
Therefore, sunscreens are only one step in the sun protection process. Using protective hats, clothing, and sunglasses is essential, as well as limited total UV exposure time.
What is the difference between physical and chemical sunscreens?
Sunscreens are usually divided into two categories: physical or chemical.
Chemical sunscreens such as para-aminobenzoic acid, benzophenones, and cinnamates when applied to the skin absorb UV radiation and convert it into harmless forms of energy.
Physical sunscreens lie on top of the skin and create a physical barrier to UV radiation. Zinc oxide and titanium dioxide are examples of physical sunscreens. Traditionally, these sunscreens are opaque (white) and were used mainly on noses/lips. More recently, nano technology has been able to create smaller molecules and hence produce a clear physical sunscreen that does not appear white on the skin. The advantages of physical sunscreens is that they:
- reflect/scatter UV radiation rather than absorb it
- are not absorbed by the skin and thus provide longer lasting protection
- cause less allergic irritations than chemical sunscreens
Examples of physical sunscreens include;
- Osmosis Shade (zinc oxide)
- Cosmedix Pure Protection (zinc oxide and titanium dioxide)
- Cosmedix Reflect (titanium dioxide)
Making that first phone call can be a confronting task – many of our patients have preferred filling out our online enquiry form. We can then contact you with an understanding of the results you are hopeful of achieving and ensure the treatment is appropriate.