What you need to know about sunscreen

There is a profusion of articles in today's Globe and Mail on different aspects of the thorny issue of sunscreen.
A quick trip to the supermarket or pharmacy will be enough to show what a proliferation of different brands, types and claims of sunscreens there exists these days. There are myriad different SPFs; UVA, UVB and broad-spectrum sunscreens; physical and chemical sunscreens; PABA and PABA-free sunscreens; water-resistant, sports, and active use sunscreens; no-rub and non-greasy sunscreens; sprays, lotions, gels and sticks; etc, etc. We are using more and more sunscreen, and yet skin cancers are still on the rise (some 6,800 Canadians were diagnosed with melanoma skin cancer in 2015, and about 1,150 died from it; another 78,000 more were diagnosed with non-melanoma skin cancers). Some studies have shown that certain sunscreens cause severe medical problems in test rodents, and yet most health authorities and cancer charities assure us that sunscreens are perfectly safe and advisable.
So, what is a person to do? First, then, a very quick primer.
SPF (sun protection factor) is a measure of how much UVB radiation penetrates the skin. SPF15, for example, means that only 1/15 of the UVB reached and penetrates the skin, while the other 14/15 is blocked by the sunscreen. What that means in practice is that it should take 15 times longer for your skin to burn when you are wearing an SPF15 sunscreen than if you were wearing no sunscreen at all. The higher the SPF, therefore, the better, although there are diminishing returns as the SPF gets higher (for example, SPF30 blocks all but 3% of UVB, while SPF60 block all but 2%). SPFs of up to 100 are available nowadays, but most advisory groups recommend an SPF of at least 30.
For that matter, what is UVA and UVB. UVB is medium wavelength ultraviolet radiation, most of which is absorbed by the earth's ozone layer, but the UVB radiation that does get through is the most destructive and is typically what causes most skin cancers. Longer wavelength UVA radiation penetrates deeper into the skin, and mainly causes aging skin and wrinkles, but it can also contribute to skin cancer. (UVC is the shortest wave ultraviolet light, which is completely absorbed by the atmosphere before it can reach us). "Broad-spectrum" means UVA and UVB, and this is the best recommendation if available.
Physical sunscreens (sometimes called "natural" sunscreens) use tiny particles of ingredients like zinc oxide and titanium dioxide to reflect ultraviolet rays so that they do not penetrate the skin at all. Chemical sunscreens use chemical filters such as PABA (4-aminobenzoic acid), retinyl palmitate, oxybenzone or avobenzone to absorb ultraviolet rays in the skin and to alter their properties. Most cancer organizations do not recommend one type over the other and leave it up to personal preference. Some people find the texture of physical sunscreens off-putting; on the other hand, some people's skins may be particularly sensitive to certain chemicals like PABA or the alcohol used in certain creams. Although some studies on rats, etc, have shown various sunscreen ingredients to be damaging in extreme concentrations, normal everyday use has not been shown to present any dangers, and certainly the alternative - no sunscreen at all - is a much greater and proven risk. Skin cancer and dermatology experts like Yale's Dr. David Leffell feel able to state categorically, "None of the approved ingredients [in sunscreens] have been shown to cause any problems in humans."
When using sunscreens, most people only apply about a third to a half of what they should, even when using creams, gels or lotions. Sprays, however, are much less efficient in covering the skin properly (and also relatively expensive because of all the wastage), and are generally less recommended. You don't need to apply sunscreen 15-30 minutes before going into the sun, as many brands used to counsel, but you should make sure to reapply it at least every couple of hours or as directed on the bottle, especially if you go in the water (even water-resistant sunscreen is not completely waterproof, and it will wash off over time).
UV-blocking clothing is another option, and modern sun-protective sportswear (utilizing special fabrics, dyes and chemical treatments) is much more breathable, lightweight and stylish than it used to be. Clothing blocks both UVB and UVA rays, and UV-blocking clothing often uses a UPF (ultraviolet protection factor) measure, rather than just SPF (which only measures UVB protection). In general, synthetic fabrics like polyester block UV better than natural fabrics like cotton. A standard white t-shirt, for example, might only have a UPF of about 7, while some sun-protective clothing has a UPF of 50+ (i.e. it blocks over 98% of harmful rays).
General advice, therefore, seems to be: look for a water-resistant, broad-spectrum sunscreen with an SPF of at least 30, and reapply regularly as directed, especially if it gets washed off by water. Don't get too caught up in this ingredient or that ingredient - the risk to humans is extremely small, and the products are heavily regulated by Health Canada and other watchdog organizations. Make sure to apply a lot of lotion (probably more than you think is necessary), and avoid inefficient sprays. If possible, avoid direct sunlight during the peak hours of 11am to 3pm, and preferably cover up with a hat and clothing if you do need to be out during that time.