Although Mother Nature’s attempt to force autumn upon us may be unreciprocated, the sad truth is that summer is just about over; and with summer, for many, came sun cream. From SPF 15 to 75, spray applications and liquid form, the majority of Britons smother themselves throughout the summer months. So, why is sun cream so important and, furthermore, how does it protect us from the dangers of the sun?
Most are aware that sun cream holds prowess in protecting us from the sun- and thus, skin cancer. Despite the onslaught we get from articles and letters home to parents of school children over the dangers and precautions regarding the sun, Vitamin D is very important for our skin. With the dangers of the sun come the benefits. Vitamin D is essential for bone development and strength. Rickets, and problems with the immune system, which can result in multiple sclerosis later on in life, are symptoms of Vitamin D deficiency, according to the UK’s National Institute for Health and Care Excellence (NICE). NICE also state that as long as people do not get burnt, it should be encouraged for us to soak up the rays.
Our sun phobia seems to stem from the disconcerting statistics, where sun exposure and skin cancer rates are proven to be positively correlated. Sun cream works against this. A mixture of organic ingredients such as octyl methoxycinnamate (OMC) or oxybenzone and inorganic ingredients such as zinc oxide or titanium oxide allow sun cream to absorb UV radiation, dissipating it as heat and to reflect or scatter the UV radiation. UV-A and UV-B both cause sunburn, and damaging effects such as skin cancer, premature aging and moles. UV-A has the longest wavelength, and is not absorbed by the ozone, causing more long term effects such as wrinkles. It also penetrates the skin further than UV-B, which is partially blocked by the ozone and is the primary culprit for sunburn.
It is worth noting that the SPF, or sun protection factor, of a sun cream only refers to the protection against UV-B rays, and so it is important to choose a broad spectrum sun cream, that protects you from both UV-A and UV-B.
Dermatologists suggest using a sun cream with an SPF of 15 or 30, rather than a higher SPF as they misleadingly don’t give much more protection. So, what do the SPF values mean? Well, if your skin would normally burn after 10 minutes in the sun, applying an SPF 15 sun cream would allow you to stay in the sun without burning for approximately 150 minutes (a factor of 15 times longer). This is a rough estimate that depends on skin type, intensity of sunlight and amount of sunscreen used. It is recommended to reapply sun cream every two hours.
The SPF scale is not linear; SPF 15 blocks 93% of UV-B rays, SPF 30 blocks 97% UB-B rays and SPF 50 blocks 98%. Another way to look at this is to think that SPF 15 allows 7 out of 100 photons to enter the skin cells. When a photon with sufficient energy strikes an atom with just the right energy, an electron can be promoted and bring the compound into an excited state. At a certain energy threshold, the electron is promoted to the point where it is completely removed from the atom, causing ionisation. The damaging effects of ionisation can lead to DNA mutations that can potentially result in the induction of cancer.
Exposure to the UV-A radiation causes production of melanin, a natural pigment which is then capable of dissipating up to 99.9% of UV radiation, as described in a 2004 paper by Meredith and Riesz. Lighter-skinned people, while building up some protection during initial sun exposure, cannot produce melanin quickly enough to dissipate all of the UV light, and their skin does eventually burn.
So next time you are thinking about buying sun cream, look out for one labelled as ‘broad spectrum’. Ensure you apply the recommended amount (2 milligrams per square centimetre, which is typically more than the average person actually applies) every two hours or after any aquatic activity, for the best protection against the damaging effects of the sun.