Chemistry hits the beach

In our society it’s a given that suntans look attractive, and it’s also understoud that they can be harmful, and downright unhealthy. So what does this mean? This means that there is a multi-million dollar a year industry that researches and manufactures UV absorbing and blocking lotions that are designed to prevent skin damage from tanning and burning. It is a prime example of the use of chemistry to improve the quality of life for many people, writes Wyn Locke.1
Our obsession with getting tanned, has boomed since the 1970s, and the outbreak of packaged tours. The “tan now” and “hurt later” philosophy has led to the sun-worshipping of everyone from the golden gods to the fair-skinned “burn ‘n peelers”, which results in a copious amount of lotions and creams being slathered on everyday. These lotions are, usually, sunscreens or sunblocks, meant to protect us from the blisters, the pain, and in general to keep our youthful glow lasting just a few years longer.

A sunguard is a cream designed to protect one’s skin from being sunburned. Our bodies are incrementally damaged by each new exposure to the sun, and this damage can later be seen in the form of wrinkles, blotchy skin and even skin cancer. Sunscreens have evolved a goodly amount over the years. Christopher Columbus noticed in 1492 that the natives of Hispaniola would protect themselves with red paint, as to avoid sun damage. The ancient Greeks, who trained for the Olympics in the nude would rub themselves with a mixture of sand and oil, which provided an opaque protection from the sun, and were sweat resistant. These notions resemble those of earlier modern day technologies. The minerals most often used in conjunction are either oxide of zinc of titanium. These are the sunscreens that graced the noses of every red suited lifeguard in the 50s.

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Today’s modern world, demands an absorbing lotion, one that protects the skin, but avoids the look of being painted like a clown. A notion so simple as a transparent, UV ray blocking or absorbing protection, isn’t quite as simple as first suspected. Firstly we must understand which compound will do this best, and to understand that, we must know what it is protecting us from. There are three types of UV rays, UVA, UVB, and UVC. UVA rays have the lowest energy, they are found having wavelengths of between 320 and 400 nanometers, and account for 90% of the UV rays which reach the earth. They cause little burning, but penetrated deeply into the epidermis, and are therefore the cause of early aging due to sun exposure. UVB rays are slightly higher in energy, and account for the remaining rays which reach the earth. They have wavelengths of between 290 and 320 nanometers and are the primary burning and tanning rays. These are the highest contributors to skin cancer. Lastly are UVC rays, which do not often reach the earth, due to the Ozone layer. They have wavelengths between 200 and 290 nanometers and can burn our skin quite intensely. We are only at risk of them where the Ozone has depleted, although this problem is growing at an exponential rate. Knowing all of this, we can estimate that the ideal sun protection cream should strongly absorb or block UV radiation in the 290 – 400 nanometer range, screening out UVA and UVB. It should be nontoxic, non-staining, odourless, waterproof, sweat-proof and… inexpensive !
The first widely available sunscreen in the 1920s was PABA (p-aminobenzoic acid). This was a good absorber of UVB light, but didn’t bode well with UVA. It’s other problems included it’s solubility, it’s tendency to irritate skin and to stain clothing. The next big break through didn’t occur until the 1970s when the carboxylic acid group was functionalised with a long chain aliphatic alcohol. This change had no effect on it’s absorption factor, but it was suddenly waterproof ! These PABA esters were also much less irritating to our skin.

In the 80’s a cry of distress was emitted by the public when it became understoud that some types of sunscreen may cause DNA damage and mutations (in short, cancer). The report indicated that one PABA exter, Padimate-O could degrade to form potentially carcinogenic products, N-nitrosamines. Although there turned out to be no reported case of mutations, cancers, or anything else related to this, these formulas are almost nonexistent within today’s brands.

The most modern sunguards are known as “Full Spectrum Absorbers”, meaning that they absorb both UVA and UVB. The first molecules used where Oxybenzone and Octocrilene. The second being a fantastic waterproofing agent, and is considered one of the safest sunscreen ingredients today. These two molecules are active ingredients, but they must also be combined with other compound that between them cover the range of 290 – 400 nanometers. These sunscreens work by a process called Vibrational Relaxation, which is when a photon is abosorbed then promoted from it’s ground state to its excited ste where it then undergoes very rapid vibrational relaxation back to its ground state. Once this has occurred, it’s in the state of Vibrational Decay. These molecules are based on salicylic acid, and often cinnamate esters. Modern oil-based sunscreen formulations contain moisturizers and vitamins that claim extra skin protection.

Now that we understand how they works, we must choose one to best suit our interests. First one must always look at their Sun Protection Factor – their SPF. This is calculated by dividing the “time taken to burn if wearing sunscreen” by the “time taken to burn if not wearing sunscreen”. This means that a compound with an SPF 45 will allow you to stay in the sun 45 times longer than if it wasn’t worn. Any SPF above 15 is considered a sunscreen. Lastly it must be said that no tan is a healthy tan, everyone should be cautious and even if you don’t believe that you “burn” you should still protect yourself from the damaging UV rays emitted from our sun.