1 in 5
At least one in five Americans will develop skin cancer by age 70. This is a US figure, cited by the Skin Cancer Foundation.6
Research Desk · Sunlight
Sunlight and your skin: vitamin D, aging and skin cancer risk.
Sunlight makes vitamin D in your skin. The same ultraviolet light also ages skin and can cause skin cancer. This guide separates the two, uses Canadian data where it exists, and cites every claim.
The short answer
- Sunlight is both necessary and harmful. UV light from the sun triggers vitamin D synthesis in the skin,2 and UV radiation is a carcinogen and the most preventable cause of skin cancer.2
- UVA is most of the UV that reaches the ground. It makes up about 95% of it, and it penetrates deeper into the skin than UVB.1
- In Canada, winter sun usually cannot make enough vitamin D. Statistics Canada reports that from late October to early March very few UV rays reach the earth’s surface.3 Zwicker (2015) notes the sun is too low in winter for vitamin D synthesis.4
- Protect with broad-spectrum sunscreen. Use SPF 30 or higher, reapply every two hours, and add shade and UPF clothing, because no sunscreen blocks all UV.89
01 · The light
Two kinds of UV, two depths.
Two ranges of ultraviolet light matter for skin. UVA is 315 to 400 nanometers and UVB is 280 to 315 nanometers.1 UVC is blocked before it reaches the ground.1
| UVA | UVB | |
|---|---|---|
| Wavelength | 315–400 nm1 | 280–315 nm1 |
| Share of UV at the ground | About 95%1 | The remainder. Most UVB is filtered by the atmosphere.1 |
| How deep it goes | Into the deeper layers of the skin1 | Cannot penetrate beyond the superficial skin layers1 |
| Skin aging | Contributes to skin aging and wrinkling1 | Enhances skin aging1 |
| Skin cancer | May enhance the development of skin cancers1 | Significantly promotes the development of skin cancer1 |
95%
- UVA: about 95% of the UV that reaches the surface (WHO).1
- UVB: the remainder. Most UVB is filtered by the atmosphere (WHO).1
UVC does not reach the Earth's surface (WHO).1
02 · Vitamin D
Why sunlight matters, and why Canadian winters are different.
UV rays from sunlight trigger vitamin D synthesis in the skin.2 Most people in the world meet at least some of their vitamin D needs through sun exposure.2
How much vitamin D the skin makes depends on how much skin is exposed, the time of day, the season, latitude and skin pigmentation.3 People with darker skin have more difficulty getting enough vitamin D from sun exposure.3
Share of Canadians aged 3 to 79, by serum 25(OH)D level.3
10%
25%
65%
- Below 30 nmol/L · 10%
- Risk of vitamin D deficiency (about 12 ng/mL).
- 30 to under 50 nmol/L · 25%
- Potentially inadequate (about 12 to 20 ng/mL).
- 50 nmol/L and above · 65%
- Sufficient for practically all people (20 ng/mL or more).
Cut-offs are from Health Canada and the Institute of Medicine, as cited by Statistics Canada.3 The NIH uses the same thresholds in ng/mL.2 1 ng/mL = 2.5 nmol/L.
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Very few UV rays reach the surfaceOutside that window, sunlight is usually enough for vitamin D (spring and summer)
Shading is approximate, by whole month. Statistics Canada: in fall and winter, from late October to early March, “very few UV rays reach the earth's surface.”3 The University of Calgary's Zwicker (2015) adds that the sun is too low in the sky for vitamin D synthesis during Canadian winter months, and that most of Canada lies north of the 42nd parallel.4 Edmonton is well north of that line.
Solar noon altitude at about 53.5° N, calculated as 90° minus the distance from the solar declination to the latitude.
December solsticeabout 13°
Shortest, lowest sun
Equinox (March, September)about 37°
Mid-season
June solsticeabout 60°
Longest, highest sun
This is a calculation from latitude and the sun's declination, not a measurement. Statistics Canada lists time of day, season and latitude among the factors that affect vitamin D made from sun exposure.3
What this means for you. No single number of minutes in the sun works for everyone. Because skin type, season and latitude all change the result,3 whether you need a supplement is a question for a doctor or pharmacist, who can check your blood level. Our research desk does not recommend vitamin D doses.
03 · Skin aging
How UV ages the skin.
The WHO says UVB enhances skin aging, and UVA contributes to aging and wrinkling.1 This is often called photoaging: skin aging driven by sun exposure rather than time alone.
The Skin Cancer Foundation cites a study finding that an estimated 80% of visible skin aging in Caucasian women is caused by the sun.6 The same source reports that women who used sunscreen daily showed 24% less skin aging than those who did not.6 Both figures come from specific study populations, so treat them as estimates.
Diet is a separate factor we study. Our AGE food rankings measure dietary advanced glycation end-products (AGEs) in 490 foods, and cooking with dry, high heat produces far more of them. See the AGE food rankings.
Our guide The Truth About Wrinkles tests the famous “80% sun” claim against the research.
04 · Skin cancer
How UV raises skin cancer risk.
Doubles
The Skin Cancer Foundation reports that a person’s melanoma risk doubles after more than five sunburns, citing a 2001 study by Pfahlberg and colleagues.6
UV radiation is a carcinogen, and UV exposure is the most preventable cause of skin cancer.2 The WHO says UVB significantly promotes the development of skin cancer, and UVA may also enhance it.1
For melanoma, the American Cancer Society says frequent severe sunburns as a child or teen increase the risk as an adult, and that melanoma can appear many years after the DNA damage was done.7 Tanning-bed use has been linked with increased melanoma risk, especially when it starts before age 30.7
05 · Protection
Protection that holds up.
Use enough.8
Most adults need about 1 ounce, roughly a shot glass, for the body. For the face, use at least 1 teaspoon.
Add shade and clothing.9
No sunscreen can block 100% of UV rays. Seek shade and wear sun-protective clothing with a UPF label.
0–2
Low
3–5
Moderate
6–7
High
8–10
Very high
11+
Extreme
The scale is set by the WHO, UNEP and WMO and published by ICNIRP, with these bands and colors.5 For today's reading in your area, check your local UV index forecast.
Our DermaGlass® masks are skincare, not sunscreen. They do not replace the protection described above.
06 · Questions
Frequently asked questions.
Is sunlight good or bad for skin?
Both. UV light from the sun starts vitamin D production in the skin. UV radiation is also a carcinogen, and UV exposure is the most preventable cause of skin cancer. It contributes to skin aging as well. 12
Can I get enough vitamin D from the sun in Edmonton in winter?
Usually not. Statistics Canada reports that from late October to early March very few UV rays reach the earth’s surface. Whether you need a supplement depends on your blood level and your health, so ask a doctor or pharmacist. 34
Do UVA or UVB cause skin aging?
Both. The WHO says UVB enhances skin aging and UVA contributes to aging and wrinkling. UVA penetrates into the deeper layers of the skin. 1
How much sunscreen should I use?
About 1 ounce, roughly a shot glass, for the whole body, and at least 1 teaspoon for the face. Choose SPF 30 or higher and reapply every two hours, and immediately after swimming or sweating. 8
Does sunscreen block all UV?
No. No sunscreen can block 100% of UV rays, so the American Academy of Dermatology also recommends seeking shade and wearing sun-protective clothing with a UPF label. 9
Is indoor tanning a safe alternative?
Tanning beds and sunlamps emit UV rays. The American Cancer Society says they can cause long-term skin damage, and tanning-bed use has been linked with an increased risk of melanoma, especially when it starts before age 30. It does not rank them against sun exposure. 7
Does sunburn in childhood matter?
Yes. The American Cancer Society says frequent severe sunburns as a child or teen increase the risk of melanoma as an adult. The Skin Cancer Foundation reports that a person’s melanoma risk doubles after more than five sunburns, citing a 2001 study by Pfahlberg and colleagues. 67
How much sun do I need for vitamin D?
There is no single reliable number of minutes. Statistics Canada lists how much skin is exposed, time of day, season, latitude and skin pigmentation as factors, and says people with darker skin have more difficulty getting enough vitamin D from sun exposure. 3
Keep reading
- The Research Desk: food datasets from the same team.
- AGE food rankings: 490 foods, measured for advanced glycation end-products.
- The Truth About Wrinkles: what actually ages skin, and what helps.
- The ingredient library: every DermaGlass® ingredient, with its evidence grade.
- Vanu Health FAQ: masks, Rosewater, books and data.
Related research and reading
- Skin Whitening: what the clinical trials show, and the rules in Canada and the US.
- Blue light and your skin: pigmentation, screens versus sunlight, tinted sunscreen.
- Seasonal skincare: how skin changes across spring, summer, autumn and winter.
- Types of light therapy: LED, lasers, IPL, UVB, PDT and cold plasma.
- The Rise of Blue Beauty: what skincare washing into the ocean means, and the rules on claims.
- The Truth About Wrinkles: a book from the Vanu Health library.
- The Accidental Discovery of Redlight Therapy: a book from the Vanu Health library.
- Research Desk sources: every reference, organised by guide.
- The Research Desk: all guides and datasets.
Sources
Where every claim comes from.
Numbers in brackets link to these entries. Each was read at the link above; the date shown is the one the source gives.
All sources across the Research Desk are collected, by page, in the master source list.
- [1] World Health Organization. Radiation: Ultraviolet (UV) radiation, questions and answers. 9 March 2016.
- [2] NIH Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals.
- [3] Statistics Canada. Vitamin D levels of Canadians, 2012 to 2013 (Canadian Health Measures Survey). 2014 (archived fact sheet).
- [4] University of Calgary, School of Public Policy. D-fence Against the Canadian Winter: Making Insufficient Vitamin D Levels a Higher Priority for Public Health (J. Zwicker). 2015.
- [5] ICNIRP, with WHO, UNEP and WMO. UV Index scale.
- [6] Skin Cancer Foundation. Skin Cancer Facts & Statistics (cites Stern 2010, Flament 2013, Hughes 2013, Pfahlberg 2001).
- [7] American Cancer Society. Causes, Risk Factors, and Prevention of Melanoma Skin Cancer. Last revised 12 August 2026.
- [8] American Academy of Dermatology. How to apply sunscreen.
- [9] American Academy of Dermatology. 5 common sunscreen mistakes, and how to avoid them.
This page is general health information from the Vanu Health Research Team. It is not medical advice and does not replace a conversation with a doctor or pharmacist. Last updated October 25, 2026.