Protecting Your Skin from the Sun

The Sun and Your Skin: The Evidence

Why Sunlight Is Good for You — in Moderation

The sun's UVB rays trigger the production of vitamin D in the skin, a hormone-like molecule essential for calcium absorption, bone strength, immune function, and potentially protection against certain internal cancers.^1,2 In Canada's northern latitude, the sun angle from October through March is insufficient to generate meaningful cutaneous vitamin D synthesis, making summer sun exposure particularly valuable for building vitamin D stores.³ Sun exposure also regulates the body's circadian clock via the eyes and skin, promotes serotonin release, and contributes to overall well-being.²

Why Too Much Is Harmful

Ultraviolet radiation is classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC).⁴ It is the leading preventable cause of skin cancer. The UV spectrum is divided into two clinically relevant ranges:

• UVB (wavelengths 280–315 nm): Causes sunburn (erythema), directly damages DNA in skin cells, and drives the development of squamous cell carcinoma (SCC) and melanoma. It is the primary driver of vitamin D synthesis.
• UVA (wavelengths 315–400 nm): Penetrates more deeply into the dermis, generates reactive oxygen species that cause indirect DNA damage, and is the main driver of photoaging (wrinkles, uneven pigmentation, loss of elasticity). UVA is present at relatively constant intensity throughout daylight hours, year-round, and passes through window glass.^4,5

Skin Cancer: What You Need to Know

Skin cancer is the most common cancer in Canada. Approximately one in seven Canadians will develop some form of skin cancer in their lifetime, and rates have been rising steadily for decades.⁶ The three main types are:

• Basal cell carcinoma (BCC): The most common skin cancer (~80% of cases). Usually slow-growing and rarely metastasizes, but can be locally destructive if neglected. Strongly associated with cumulative UV exposure.^6,7
• Squamous cell carcinoma (SCC): More aggressive than BCC, with a small but meaningful risk of spread. Arises from chronic UV damage and actinic keratoses (pre-cancers).⁷
• Melanoma: Accounts for fewer than 5% of skin cancers but the large majority of skin cancer deaths. Associated with both chronic UV exposure and intermittent intense exposure (sunburns), particularly in childhood and adolescence.^8,9

Most skin cancers are highly treatable when caught early. The best strategy is to prevent them through sun protection, and to detect them promptly through regular skin self-examination and — for higher-risk individuals — periodic clinical skin examinations.

Strategy 1: Timing and Shade

UV radiation intensity is not constant throughout the day. It peaks when the sun is highest in the sky and is greatly reduced in the early morning and late afternoon. In Canada, this peak window falls roughly between 10:00 AM and 4:00 PM (or 11:00 AM–5:00 PM during Daylight Saving Time).¹⁰

Seeking shade — trees, awnings, umbrellas, covered patios — meaningfully reduces UV exposure, though it does not eliminate it entirely. Reflected UV from sand, water, snow, and concrete can still reach you in the shade, accounting for up to 80% of ambient UV on some surfaces.^10,11 Shade is most effective as a component of a layered approach.

The UV Index: Your Daily Tool

Environment and Climate Change Canada publishes a daily UV Index (UVI) forecast, which ranges from 1 (low) to 11+ (extreme). In Kelowna and the southern BC interior, the UVI regularly reaches 8–10 in summer, placing it in the "very high" range for several hours each day.^3,10

Source: Health Canada / Environment and Climate Change Canada UV Index categories.¹⁰

Strategy 2: Protective Clothing — The First Line of Defence

Clothing provides a reliable, consistent physical barrier that does not "wear off," wash off, or require reapplication. It is the most dependable form of sun protection available.^11,12 Clothing should be considered the foundation of your protection strategy, with sunscreen used to cover what clothing cannot.

What Makes Clothing Protective?

• UPF Rating: Look for the Ultraviolet Protection Factor (UPF) label. A UPF of 50 allows only 1/50th (~2%) of UV radiation to reach the skin. For reference, most standard white cotton T-shirts have a UPF of only 5–8 — less than SPF 10 sunscreen.¹²
• Fabric construction: Tightly woven fabrics (polyester, nylon, denim) block more UV than loosely woven materials. Dark or bright colours generally absorb more UV than light colours. Synthetic fibres typically outperform natural fibres.¹²
• Wet fabric: Some fabrics lose significant UPF protection when wet (especially light cotton). UPF-rated swimwear and rash guards maintain their protection when wet and are particularly valuable for children at the beach or pool.

Hats and Eyewear

• Wide-brimmed hats (≥7.5 cm / 3 inches): Protect the face, ears, and back of the neck — areas that account for a disproportionate share of BCCs and SCCs due to chronic incidental sun exposure. Baseball caps leave the ears and neck largely unprotected.¹¹
• UV-blocking sunglasses: Look for lenses labelled "100% UV400" protection. UV radiation to the eyes contributes to cataracts, pterygium, and ocular surface melanoma. Wrap-around frames offer better protection than standard frames.¹³

Strategy 3: Sunscreen — Understanding the Evidence

Sunscreen is an important tool but is most effective when used correctly and combined with other strategies. The evidence supports meaningful reduction in SCC risk and actinic keratoses with regular sunscreen use; evidence for melanoma prevention, while plausible, has been harder to definitively demonstrate in randomized trials due to the long latency of the disease.^14,15

Mineral vs. Chemical Sunscreens

SPF: What It Means and What It Doesn't

Sun Protection Factor (SPF) specifically measures protection against UVB only — the rays responsible for sunburn. SPF 30 blocks approximately 97% of UVB radiation; SPF 50 blocks about 98%.¹⁴ No sunscreen blocks 100%. It is important to note that SPF does not directly measure UVA protection — this is why the "broad-spectrum" label matters. A broad-spectrum product has demonstrated meaningful protection against both UVA and UVB as tested by Health Canada standards.

How to Apply Sunscreen Correctly

Correct application is where sunscreen most commonly fails in practice. Studies consistently show that people apply only 25–50% of the recommended amount, which reduces the effective SPF dramatically — an SPF 50 product applied at half the recommended quantity may deliver protection equivalent to only SPF 7–10.^14,15

• Amount: Use approximately 30 mL (one shot glass, or a large tablespoon) for the full body, and a dime-to-quarter-sized amount for the face and neck alone.
• Timing: Apply chemical sunscreens at least 20 minutes before going outdoors. Mineral sunscreens work immediately.
• Reapplication: Reapply every 2 hours, and immediately after swimming, sweating, or towelling off — regardless of "water-resistant" claims. Water resistance only means the product retains SPF for 40–80 minutes in water, not that it lasts indefinitely.¹⁴
• Don't forget: Ears, back of the neck, tops of the feet, the scalp (use a spray product or UPF hat), and the lips (an SPF 30 lip balm).
• Expiry: Sunscreen expires, typically after 2–3 years. Discard if it has changed colour, smell, or consistency.

Special Populations and Circumstances

Children

Children's skin is particularly vulnerable to UV damage, and childhood sunburns carry a disproportionate long-term cancer risk. Health Canada recommends keeping infants under 12 months out of direct sunlight and using shade and protective clothing as primary strategies. For children over 6 months, a mineral sunscreen is preferred on exposed skin.¹⁷ Make sun protection a normal part of outdoor activities — not a special occasion.

Higher Fitzpatrick Skin Phototypes (Darker Skin Tones)

Melanin provides some natural UV protection: skin phototypes V–VI have a natural SPF estimated at 8–13.¹⁸ However, this does not confer immunity from UV damage or skin cancer. Melanoma in darker-skinned individuals is often diagnosed later (frequently on non-sun-exposed sites such as the palms, soles, or under nails) and carries a worse prognosis, partly due to diagnostic delay.¹⁸ Sun protection remains important for people of all skin tones.

Photosensitizing Medications

Many commonly prescribed medications can significantly increase UV sensitivity, making sunburn, rash, or photo-distributed skin reactions more likely at lower UV doses. Common examples include: tetracyclines (doxycycline), fluoroquinolones (ciprofloxacin), thiazide diuretics (hydrochlorothiazide), certain antifungals (voriconazole), amiodarone, and some NSAIDs. If you take any of these medications, sun protection is particularly important. Ask your doctor or pharmacist whether any of your medications are photosensitizing.¹⁹

Vitamin D Supplementation in Canada

Given Canada's northern latitude and long winters, Health Canada recommends that adults over 50 take a daily vitamin D supplement of 400 IU, and many clinicians — including in BC — recommend 1,000–2,000 IU for adults of all ages in view of widespread insufficiency in northern climates.³ This is a practical, safe, and evidence-based way to maintain vitamin D status without depending on unprotected sun exposure.

Skin Self-Examination: Know Your Skin

The best tool for early detection of skin cancer is familiarity with your own skin. Monthly self-examination — best done after a bath or shower in good light, using mirrors to check the back and scalp — allows you to notice new or changing spots early, when treatment is most effective.²⁰

The ABCDE Rule for Moles and Spots

A Practical Sun Protection Plan

The Bottom Line

Sun protection is not about fear of the outdoors — it is about making informed, practical choices that allow you to enjoy the benefits of outdoor activity while minimizing the well-documented risks of UV overexposure. Skin cancer is extremely common, largely preventable, and almost always curable when caught early. A layered approach — timing, shade, clothing, and sunscreen used correctly — provides far better protection than any single strategy alone.

The most important steps are often the simplest: wear a hat, seek shade during the midday peak, use sunscreen consistently rather than occasionally, and know your own skin well enough to notice when something changes.