H ow do you choose your sunscreen? In a conclusive study conducted on four of my male cycling friends, it appears to be by the colour of the tube.

Ten days ago, during our week of July in May and at a drive-to ride beginning in Cayuga, none of us had remembered to bring sunscreen. All that was available were a couple of mostly used-up tubes of dollar store suntan lotion that had spent the winter in my van. One tube was a cute pink, the other a more masculine orange. Both were marked SPF 30 in print bold enough that we could all read it without our glasses. When the two tubes were offered to the guys, every one chose the orange without questioning ingredients or protection.

Getting past the colour of the tube to understand sunscreen, what it can and cannot do, the different types available and the advantages and disadvantages of each, can make significant long- and short-term differences in the health of your skin, and how likely you might be to contract one of the three most common types of skin cancer: squamous cell carcinoma, basal cell carcinoma, and melanoma. The Canadian Cancer Society estimates that in 2022 some 9000 Canadians will be diagnosed with melanoma, the most common but least deadly form of skin cancer. Twelve hundred will die from it—770 men and 440 women.

Melanoma originates in our melanocyte cells, most of which are located in our skin. Cancer occurs when melanocyte cells grow uncontrollably and develop into tumours which most frequently present on the back of men and back and legs of women.

The National Cancer Institute of United States says the rate of new cases has tripled since the 1970s, and lists ultraviolet A (UVA) radiation and severe sunburn as major contributing factors.

To choose sunscreen wisely, it’s important to know that the sun emits two distinct types of ultraviolet light. Each reacts differently with our skin and causes different long-term health effects.

UVA light has a longer wavelength which can penetrate into the dermis, our thickest layer of skin. Skin aging, wrinkles, and immune system suppression can result from unprotected exposure to UVA rays.

UVB rays have a shorter wavelength, and are the rays associated with burning the top layer of skin. The resultant sunburn, and hence UBV rays, play a key role in causing skin cancer and permanent skin damage over time.

The protective ingredients found in sunscreen lotions are classified in two main groups.

Sunscreen that includes physical blockers protects us by reflecting and scattering UV rays away from our skin. Sunscreens that use chemical blockers protect by absorbing the sun’s UV rays and converting them to heat.

Physical blockers usually include two active mineral ingredients, zinc oxide and titanium dioxide, which are classified by Health Canada as natural ingredients. Sunscreens which contain only physical blockers can be identified by an eight digit natural product number (NPN) on their packaging.

A recent trend in manufacturing sunscreen containing physical blockers is to reduce, or micronize, their mineral compounds to nanoparticles. This process makes the sunscreen easier to apply and allows it to disappear into the skin, eliminating the greasy white residue of past suntan lotions. Studies have shown that these nanoparticles do not penetrate our bodies beyond the skin or enter our blood stream, so they are unlikely to create additional health risks.

Sunscreens using chemical blockers such as avobenzone, homosalate, octocrylene, octisalate, octinoxate and oxybenzone are classified by Health Canada as having drug ingredients, and carry a drug identification number (DIN) on the label similar to other non-prescription drugs. Some small studies conclude that these chemicals may soak through our skin, as evidenced by high concentrations found in human blood, urine and breast milk. This is especially common in people that apply large amounts of sunscreen to their skin.

Health Canada acknowledges more studies are needed, but at this time they are following American FDA guidelines which claim sunscreen absorption doesn’t pose a risk and that any of the chemical ingredients currently found in sunscreen are safe for use.

Sunscreens labeled “broad spectrum” contain both physical and chemical blockers, which means they are effective in blocking both UVA and UVB rays, maximizing overall protection from the sun. In Canada broad spectrum sunscreens are labeled with a DIN number.

It’s important to recognize that a sunscreen’s SPF rating is not an indication of its ability to protect from all types of radiation.

SPF is a relative measure that compares the amount of time it will take unprotected skin to burn compared to a specific sunscreen when applied as directed on its label. SPF numbers therefore represent a protection factor related to sunburn only, not other types of skin damage such as accelerated skin aging, DNA cell damage, free radical generation, and skin cancer. If you re-apply your sunscreen at two hour intervals as recommended, an SPF rating of 30 is considered sufficient. Ratings beyond SPF 60 have more to do with marketing than protection.

Sunscreens advertised as moisture or sweat-resistant, frequently targeted toward sports participants, also need to be used with an understanding of their true capabilities.

No sunscreen is 100 percent waterproof, and labels in Canada generally caution an effective limit of 80 minutes. All sunscreens, including moisture resistant, should be applied approximately 10-15 minutes before exposure to the sun or going into water. Use of towels to dry oneself, or a sleeve or the back of a cycling or golf glove to absorb perspiration will also remove most sunscreens, reducing protection.

Does using sunblock create a risk of Vitamin D deficiency? The science says no. At peak sun times, between five and thirty minutes of exposure to sunlight each day will provide humans with sufficient Vitamin D. It is highly likely that even the most conscientious sunscreen users will find themselves exposed without protection for a sufficient time each day.

For those that hike, bike, paddle, or participate in any other sports that place them in proximity to mosquitoes, ticks and blackflies, sunscreen and insect repellent can safely be used together. Apply your sunscreen first, and give it the prerequisite 10-15 minutes before applying your choice of insect repellent over it.

Unused sunscreen deteriorates with time. On the tubes in our home the expiry date is stamped in the plastic at the bottom where the tube is heated and squished for sealing purposes.

Now that you’ve chosen the most-protective sunscreen, what is the best way to use it?

As above, apply approximately 10-15 minutes before exposure. Sunscreen breaks down in light and loses its effectiveness quickly, so re-apply every two to four hours, or more often if sweating or swimming.

In southern Ontario between 11 AM and 3 to 4 PM is when the sun is brightest and most care needs to be taken to apply sufficient sunscreen.

Applying the proper amount of sunscreen is important. Health Canada recommends a teaspoon per each arm, leg, your front, back, and face or neck. That equates to about seven teaspoons to cover all areas of exposed skin on our body, or 35 milliliters. If metric conversion isn’t your strength, using a shot glass full of sunscreen will do a complete jo b.

Turns out selecting a sunscreen that is broad spectrum, has at least SPF 30, is water and sweat resistant, and isn’t a year beyond its expiry date might have been smarter than simply going for the orange coloured dispenser. Live and learn. ◆