Sun protection: an interview with Jane Hanrahan

Interview conducted by April Cashin-Garbutt, MA (Editor)Oct 11 2012

Please could you explain what ultraviolet radiation is?

UV radiation is a form of energy being transmitted. Sunlight is main source of UV radiation, although manmade sources also exist, such as the lamps used in sunbeds. At the earth’s surface sunlight consists of approximately 2 percent UV light, 47 percent visible light and 51 percent IR light.

The UV wavelength range is from 100-400 nanometers (nm). UV radiation that reaches the earth’s surface has wavelengths between 295-400 nm, with the shorter wavelengths being blocked by the earth’s atmosphere.

How does ultraviolet B (UVB) radiation differ from ultraviolet A (UVA) radiation?

UV radiation is subdivided in to three categories, UVA (320-400 nm), UVB (280-320 nm) and UVC (280 -100 nm).

UVC radiation is very damaging to biological tissue, but fortunately doesn’t reach the earth’s surface. Although UVA and UVB rays make up only a very small portion of the sun’s rays, they are the main cause of the sun’s damaging effects on the skin.

Most of the UV radiation at the earth’s surface is UVA, with only about 5 % being UVB. UVA radiation has a longer wavelength and lower energy than UVB. UVB radiation is mostly absorbed by the epidermis of the skin, however, UVA rays penetrates more deeply to below the dermis.

What type of ultraviolet radiation was originally thought to cause damage to the skin?

It has been known for many years that UVB radiation is responsible for sunburn, and was believed to be the most damaging to the skin. As a consequence, many of the sunscreens available until the earlier 1990’s only blocked UVB. However, it is now known that although UVA radiation doesn’t cause sunburn it does cause other damage to the skin.

How does the skin damage caused by UVA radiation differ from the damage caused by UVB radiation?

UVB causes sunburn and directly damages DNA. UVA causes suppression of the immune system and is believed to be responsible for most of the signs of photo-ageing. Both UVA and UVB can cause free-radical generation, which indirectly cause DNA damage.

Which type of ultraviolet radiation is most damaging to the skin?

Both UVA and UVB radiation cause damage to the skin and contribute to skin cancer. UVA induced damage also results in the visible signs of ageing such as wrinkles and leathery skin.

What are the best ways to avoid skin damage?

The best way to avoid photo-induced skin damage is to stay out of the sun particularly in the middle of the day in summer. If it is not possible to avoid the sun entirely, then wear a broad-spectrum sunscreen with an SPF of at least 30+, wear hats and cover as much skin with sun-protective clothing and seek shade when possible. Adequate amounts of sunscreen should be applied 20-30 minutes before going out in the sun and then re-applied every two hours, or after swimming.

What is meant by the Sun Protection Factor (SPF) of a sunscreen?

The well-known SPF is determined by a highly regulated clinical test using lamps that simulate solar radiation on human volunteers. It measures the time take for a minimal erythema or sunburn to appear when sunscreen is applied compared to the minimal erythemal dose (MED) without sunscreen. So that an SPF of 30 means that if it takes 10 minutes for skin to start to burn without sunscreen it will take 300 minutes with that sunscreen.

However, the SPF only measures how effective a sunscreen is at protecting skin from UVB radiation. To ensure protection against UVA as well as UVB, a sunscreen must be labeled as broad spectrum, which means that it also meets requirements for UVA protection.

What do you think about the concerns over the long-term safety of sunscreens, in particular the worries over the absorption of nanoparticles into the skin?

A Review by a European Union scientific committee in 2001, found that chemical sunscreen ingredients don’t exert oestrogen-like effects in people. They estimated that the hormonal effects of currently approved sunscreens would need to be 100, 000 times more potent before they showed an effect in humans.

In 2009 the Australian Therapeutic Goods Administration (TGA) reviewed the literature on titanium oxide and zinc oxide nanoparticles in sunscreens concluding that the weight of all available evidence indicates that nanoparticles may be of concern if they are absorbed by the skin, but current research indicates that nanoparticles do not penetrate healthy intact skin. However, this does mean that nanoparticles may be absorbed by skin affected by wounds, dermatitis or other skin conditions.

For anyone that is worried about the chemicals or nanoparticles, there are several zinc oxide based sunscreens available that don’t contain nanoparticles.

Would you like to make any further comments?

The benefits of UV protection have been clearly established, and the use of sunscreens is an important part of protecting the skin from sun damage. Despite possible concerns about the long-term safety of UV filters, the benefits outweigh risks and sunscreens should form a part of all sun protection strategies.

That said, it is also important to remember that small amounts of sunlight is essential for the body to produce vitamin D. The amount sun required to produce adequate amounts of vitamin D depends on location, time of the year and the type of skin a person has. Anyone who is concerned about their vitamin D levels should talk to their Doctor or Pharmacist.

Where can readers find more information?

For more information about sunscreens see the article in Australian Prescriber http://www.australianprescriber.com/magazine/35/5/148/51

About Jane Hanrahan

Jane Hanrahan graduated from the University of Sydney majoring in chemistry and pharmacology in 1989. After completing a PhD in Chemistry at the University of Warwick (UK) and postdoctoral research at the Universities of Cardiff and Sydney, she was appointed to a lectureship the Faculty of Pharmacy at the University of Sydney in 2002, and promoted to Associate Professor in 2010. Her research focuses on the design, synthesis and medicinal chemistry of ligands at GABA receptors and the role of GABA receptors in disorders of the central nervous system. For the past 10 years she has taught medicinal chemistry to pharmacy students on topics including photochemotherapy, sunscreens, statins and antihistamines.