We did the math – here’s how much sunscreen you need to keep skin protected.

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We did the math – here’s how much sunscreen you need to keep skin protected.

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We all know the importance of applying sunscreen. The question is, are you applying enough? A sun protection factor (SPF) rating is the measure of the fraction of UV rays that reach the skin when sunscreen is applied. A sunscreen with SPF15, for instance, allows only 1/15 of UV rays to reach the skin, provided you use an adequate amount: roughly 2mg of sunscreen for every square centimetre of skin. Translated into tangible terms, that’s like applying a heaped teaspoon of sunscreen to the face and neck. Use this handy guide (calculated based on an average-sized adult) to make sure you’re getting the protection you paid for.  

The face, ears and neck
1: heaped teaspoon
Dot the sunscreen on the forehead, nose, cheeks, chin and neck, then use a patting motion – this reduces skin irritation – to spread it evenly across the face and neck. Be sure to apply it all the way up to the hairline, and don’t forget the ears and the eye area.

The arms
2: heaped teaspoons
Use one teaspoon for each arm. Make sure to apply the sunscreen evenly, and on the inner arms, forearms and hands, not just the upper arms.

The torso
2: heaped teaspoons
Apply sunscreen on both the front and back torso. The skin on the chest is thinner than that in other areas, so ensure you apply enough sunscreen there or you’ll start seeing the effects of sun damage (think a prematurely wrinkly decolletage!). Get a friend to help you with hard-to-reach areas, like between the shoulder blades. 

The legs
4: heaped teaspoons
You’ll need at least two teaspoons for each leg. Commonly missed areas are the back of the legs and the top of the feet, so take extra care to cover these areas. 

Quick sunscreen facts
Yes. Sprays are the most convenient, but research shows you need to spray the same area for at least four seconds to get the same amount of sun protection a lotion provides. There are also two types of sunscreen: physical and chemical, which work differently. The former usually has active mineral ingredients (think zinc oxide and titanium dioxide) that reflect the sun’s rays, while the latter has ingredients such as oxybenzone and octinoxate that penetrate the skin and absorb the sun’s rays. 

Chemical sunscreens should be applied 30 minutes before sun exposure to give the ingredients time to bind to the skin. Physical sunscreens work right offthe bat, so apply these right before you head out.

The rule of thumb is every two hours, and immediately after swimming or excessive sweating.  

Expert source: Dr Low Chai Ling, medical director at The Sloane Clinic.