Why Reapply Sunscreen Every 2 hours?

Sunscreen Protection

Sunscreen, when applied correctly, is engineered to extend the time it takes for your skin to burn based on the indicated SPF factor. In other words, if unprotected would normally burn in 5 minutes, applying an SPF50+ sunscreen extends that time to a minimum of 300 minutes, or 5 hours.

So, why do all sunscreens recommend reapplying after 2 hours, even if the product protects for many more hours, and offers 4 hours of water resistance?This is all to do with the way the product is tested (in controlled conditions) versus how we use the product in real life. 

The only SPF test method currently approved is “in-vivo”, which means sunscreen products must be tested on humans. A specialised testing laboratory directs a simulated beam of sunlight onto the back of volunteers. The SPF is determined for at least 10 individuals then averaged to establish the maximum claimable SPF.

The Australian water-resistant standard is the world’s most stringent; to reflect Australia’s renowned outdoor lifestyle in harsh climate conditions. In Australia, 4-hour water resistant SPF sunscreen will maintain full sun protection efficacy, even after 4 hours spent in a pool or at the beach.

However, the highly controlled conditions used to create a reliable test are very different from how we use sunscreens in everyday conditions.

In real life, such as at the beach, playing sports, or outdoors at work, sunscreen will be worn down by our active lifestyle. Actions such as towel drying, wiping off sweat, contact with surfaces (e.g. clothing or chairs), or the friction of waves or water when swimming, will each remove some sunscreen from our body. Also, a testing laboratory will apply sunscreen under highly controlled conditions by a trained technician. Whereas in real life our application of sunscreen may be far less perfect.

Apply Sunscreen

So how do we ensure that people do not get sunburnt in real life conditions? We recommend that broad spectrum sunscreen is liberally and frequently applied, then reapplied to ‘touch-up’ the applied sunscreen; ensuring it is functioning effectively at all times.

It can be hard to determine precisely when to reapply sunscreen, but the commonly agreed recommendation is at least every 2 hours. Remember, if you have been swimming and then towel dry, it is strongly recommended to reapply your sunscreen. Sunscreen use can vary for different skin types, so make sure to apply broad-spectrum sunscreen every day as to avoid skin cancer.