‘Slip slop slap’ has entered the national lexicon as a reminder to use a sunscreen when outdoors during the summer. The original campaign using the phrase was launched in Australia in 1981 (you can watch the original TV clip with Sid the Seagull here).

Sunscreens – and there are a wide variety available from the pharmacy – help prevent the sun’s ultraviolet (UV) radiation from reaching the skin. Two types of UV – UVA and UVB – damage the skin and increase your risk of skin cancer. UVB is the chief culprit behind sunburn, while UVA rays, which penetrate the skin more deeply, are linked to the ageing effects of sunshine

The sun protection factor (SPF) in a sunscreen is a measure of the protection you get from UVB. You should always use a product with SPF15 or higher. If it takes 20 minutes for your unprotected skin to start turning red, using an SPF 15 sunscreen theoretically prevents reddening for 15 times longer — about five hours.

But in real life no sunscreen, regardless of strength, will stay effective for more than two hours without reapplication. Also, reddening of the skin is a reaction to UVB rays alone and tells you little about what UVA damage you may be getting. So slip, slop, slap!