When it comes to sunscreen, the average consumer could be forgiven for feeling overwhelmed by the array of choices in the drugstore aisle. UBC assistant professor of dermatology and skin science Sunil Kalia sheds light on how to choose the best sunscreen, and most importantly, how to use it.
Recently consumer groups such as the Environmental Working Group (EWG) have cautioned against chemical sunscreens. What are the concerns about?
The science behind the EWG recommendations is not rigorous. They say to avoid sunscreens that contain a retinol or vitamin A agent. However, this is based on one study in which hairless rats were given extremely high UV exposure rates that aren’t comparable to regular sun exposure. In addition, the study didn’t demonstrate a causal link between retinol and skin cancer.
Currently, vitamin A agents are used commonly in over-the-counter skin products. As clinicians, we use oral retinoids in transplant patients to decrease skin cancer, and the topical form helps prevent photo aging. Another chemical that gets discussed is oxybenzone, with concerns raised that it can have hormonal effects. But the evidence we have so far has not shown it to have any clinical effects in humans.
What is the difference between a chemical and mineral sunscreen?
Both chemical and mineral sunscreens prevent UV light from penetrating the skin. Both types of sunscreen absorb ultraviolet energy to some extent. Mineral sunscreens usually contain titanium dioxide or zinc oxide, and they also block incoming radiation by reflecting it. These sunscreens appear white because light is being reflected in the visible spectrum. Chemical sunscreens primarily work by absorbing UV rays, converting them to heat, and releasing it from the skin. Checking the sunscreen label will tell you whether it’s a mineral or chemical sunscreen.
What are some common mistakes people make when using sunscreen?
Most people don’t apply enough sunscreen, nor do they apply it as frequently as they should. It should be a teaspoon each on the face and neck, each leg, arms, front, and back. The reality is that most people might apply half that amount, which gives half the protection. In addition, sunscreen tends to come off as people perspire. That’s why I recommend an SPF of 60 when individuals will be out in the sun for a prolonged period of time. And it should be reapplied every two hours.
What is the difference between UVA and UVB rays?
The acute effects of UVB rays are sunburns, whereas UVA is linked with tanning. Historically, we thought that skin cancer was primarily caused by UVB, however there is increasing evidence that UVA exposure also plays a role.
The SPF number on a sunscreen tells you how much UVB protection it provides, but it does not tell you anything about UVA protection. More work needs to be done to quantify UVA protection in sunscreens. Consumers should look for broad-spectrum coverage on sunscreen labels, which is currently the best method Health Canada recommends to ensure both UVB and UVA protection.