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Explainer: How does sunscreen work?

11 January 2017
What does SPF really mean? What does broad spectrum mean?

Professor of Dermatology, Diona Damian, brings to light everything you need to know about sunscreen, including why it's still important during the cold winter months.

How does sunscreen work?

In this video produced in association with the Sydney Morning HeraldProfessor Diona Damian explains the most effective sun protection for every season.

What is sunscreen?

“We’re told to use broad-spectrum 50+ sunscreen that fights UVA and UVB radiation,” explains Professor Damian, a Professor of Dermatology from the University’s Medical School explains.

Sunblock in the sand with 'SPF 15' and 'UVA and UVB protection' on the label.

“Sunscreen acts like a filter. It doesn’t block UV radiation completely but it can substantially reduce how much UV reaches your skin.

“Exposure to the sun, even for a few minutes, can weaken the immune system that helps fight off cancers and sun spots, making it harder for your skin to stay healthy.”

What does broad spectrum mean?

“When you see ‘broad spectrum’ on a label that means it helps filter two kinds of radiation; UVA and UVB”, Professor Damian said.

  • “UVB is short-wave radiation, and it's the one that's most responsible for sunburn.
  • “UVA has longer wavelengths, and although it's less able to cause sunburn, both wavebands can suppress our skin's immune defences against skin cancer.”  

What does SPF mean?

A sunscreen with a sun protection factor – or SPF – or 50+ increases the skin’s sunburn threshold by at least 50 times when tested in tightly-controlled lab settings, Professor Damian said.

“But labs aren’t the real world. In real life, even at the beach, people tend to apply their sunscreen much less thickly than in lab settings. The artificial lamps used for testing don’t quite recreate the UV radiation of real sunlight.

“SPF 15 sunscreen you apply while at the beach or pool might actually give you a protection factor more like 6 or 7. That's one of the reasons you should always go for the highest number you can find. In Australia, that's SPF 50+.”

Facts about sun safety

  1. Most of our vitamin D comes from the sun. Professor Damian suggests some people with extreme skin damage may need to avoid sunlight altogether, and take vitamin D supplements.
  2. Always avoid getting burnt and be sure to apply sun protection every day.
  3. It’s never too late to start using sunscreen, said Professor Diona Damian. Research shows improvements in sun-damaged skin within a few months when people start using it daily.