Let’s get one thing out of the way: you absolutely should use sun cream. Exposure to the sun’s ultraviolet rays (UVA and UVB) causes damage to the skin which can lead to skin cancer. UVB rays are the ones that cause most sunburn, but UVA rays, which penetrate deeper into the skin, also cause the skin to wrinkle, sag, get leathery and all those other signs of aging we would like to avoid. Sun creams with an SPF of 15 or higher really do protect your skin against the UVB rays, and most protect against UVA rays too – so use your sun cream!
If you really want to protect your skin, is the key to layer on the highest SPF you can get your hands on? Not necessarily. First of all, there is a 1.6 per cent or less difference between sun creams with SPF 30,45,50 and 60. Sun creams with SPF 15 block approximately 94 per cent of all incoming UVB rays. Sun creams with SPF 30 block 96 per cent of the UVB rays. Sun creams with SPF 40 block 97 per cent of the rays. The higher SPFs do block more UV rays, but it is not clear whether they are increasingly effective (in actual use) over the SPF 50 mark.
If you rely on the SPF model, you can still get your skin into lots of trouble. No sun cream, regardless of its strength, is effective for longer than two hours without reapplication. You’d be better off faithfully reapplying your SPF 15 or 30 sun cream every two hours than staying out in the sun all day with SPF 50-plus. Plus you need to use a lot of sun cream for it to be effective. You should use at least one ounce, the equivalent of one full shot glass, on the entire body. Sun cream SPF is tested using 2 mg of sun cream per square centimetre of your body, which equates to two fingers-length of product applied to each of the eleven areas of the body (i.e., head, neck and face; left arm; right arm; upper back; lower back; upper front torso; lower front torso; left upper leg; right upper leg; left lower leg and foot; right lower leg and foot). If you stayed at the beach all day, you’d have to use up almost an entire 200ml bottle of sun cream in order to follow this recommendation. Since most people don’t even come close to following the official recommendation, the level of protection they receive from their sun cream is probably half, or less than half, of what is described on the bottle.
There are other rules for sun cream application that you should follow to make sure you’re as protected as possible. You should apply your sun cream thirty minutes before you go out in the sun to let the ingredients bind to the skin. Ideally, you should apply it again twenty minutes after you go out. A study shows that this early reapplication is even better than reapplying two hours later (which is the standard recommendation). If you follow this guideline, you need to reapply the sun cream again only if you go swimming, dry off with a towel or sweat excessively.
Simply put, once you get to SPF 15 or 30 there is not a huge difference between the levels of sunscreen. There is no harm in using the highest possible SPF, but what will really make the difference for your skin is applying a thick layer of sun cream thirty minutes before you go outside and then again twenty minutes after you’ve been outdoors.