Sunscreens are topical formulations developed to protect the skin from ultraviolet (UV) radiation, a significant factor in premature skin aging and the leading cause of skin cancers such as basal cell carcinoma, squamous cell carcinoma, and melanoma. The consistent use of sunscreen, combined with other protective measures like sun-protective clothing and seeking shade, is essential for minimizing the harmful effects of UV exposure. Though terms like “sunblock” were once used, they are now discouraged because no product can block 100% of UV rays.
UV radiation is classified into three types: UVC, UVB, and UVA. UVC is mostly absorbed by the Earth’s atmosphere and does not reach the surface. UVB rays are primarily responsible for sunburn and direct DNA damage, while UVA rays penetrate deeper into the skin, contributing to photoaging and indirect DNA damage. Sunscreens are formulated to protect against both UVA and UVB rays, and Health Canada recommends daily sunscreen use when the UV Index is 3 or higher.
Sunscreens are typically divided into two categories:
Chemical sunscreens(also known as organic filters) absorb UV radiation and convert it into harmless heat. Common ingredients include oxybenzone, avobenzone, octocrylene, and homosalate. Photostable compounds like bemotrizinol and bisoctrizole are often added for improved UV protection stability.
Physical sunscreens (or inorganic filters) contain zinc oxide or titanium dioxide, which absorb and reflect UV rays. These are chemically inert, non-irritating, and photostable, making them ideal for sensitive skin and pediatric use. Micronized (nano) forms improve cosmetic acceptability by reducing the visible white residue. Health Canada considers these ingredients safe and effective when used as directed, and no evidence supports concerns about nanoparticle toxicity through intact skin.
In Canada, sunscreens are classified as natural health products or non-prescription drugs, depending on their ingredients and claims. All products must have a Drug Identification Number (DIN) or Natural Product Number (NPN) issued by Health Canada, ensuring they meet safety, efficacy, and labelling standards.
Under Health Canada’s Sunscreen Monograph, only zinc oxide and titanium dioxide are currently recognized as safe and effective physical filters for use in sunscreen products. The use of marketing terms such as “sunblock,” “waterproof,” and “sweatproof” is prohibited on Canadian sunscreen labels, as they are considered misleading; instead, products may claim to be “water-resistant,” but must specify the duration of protection, such as 40 or 80 minutes. To be labeled as offering broad-spectrum protection, sunscreens must meet specific critical wavelength criteria of at least 370 nanometres, ensuring they provide effective protection against both UVA and UVB radiation.
The Sun Protection Factor (SPF) rating refers to protection against UVB radiation:
- SPF 15: blocks approximately 93% of UVB rays
- SPF 30: about 97%
- SPF 50+: about 98%
Health Canada advises consumers to apply sunscreen generously and reapply every 2 hours, especially after swimming, sweating, or towel drying. A broad-spectrum label ensures UVA protection, typically measured through UVA-PF and critical wavelength testing.
Some chemical sunscreen ingredients such as oxybenzone and octinoxate have been restricted or banned in certain countries and regions due to their potential to damage coral reefs. Although these bans are not currently in place in Canada, individuals may choose reef-safe mineral-based sunscreens for environmental considerations.
Regarding human health, there is ongoing research into the systemic absorption and endocrine-disrupting potential of some chemical UV filters. While Health Canada and international bodies acknowledge these concerns, current evidence indicates that the benefits of sunscreen use far outweigh the theoretical risks, particularly in preventing skin cancers and photoaging.
Sunscreens are a cornerstone of any effective sun protection strategy. Understanding the differences between physical and chemical sunscreens, reading labels accurately, and following Health Canada’s application and safety guidelines will help ensure optimal skin protection. For best results, sunscreen should be part of a comprehensive sun safety routine, which includes sun-protective clothing, shade-seeking behavior, and regular skin checks for early detection of changes.
Protect your skin. Protect your health. Use sunscreen wisely.
