Effects Of Sun Exposure – Our Love/Hate Relationship with the Sun

As winter turns to spring and the weather signals snowy days are behind us, we eagerly anticipate more time with our 6 billion-year-old friend, the sun. The sunshine brings with it feelings of renewed energy, life, and summer excitement but it also creates a source of confusion for many, since we all know that excessive sun exposure is dangerous for our health. In this article, we’ll review the effects of sun exposure and the health benefits versus the risks of increased sun exposure and how best to protect yourself when outdoors.

Health Benefits VS The Risks Of Sun Exposure

First “the good”: Health benefits from increased sun exposure

Exposure to sunlight helps us sleep better, feel better, and often gets us outdoors to engage in more physical activities and sports. It also initiates the metabolic reactions which create vitamin D (a group of vitamins important for calcium absorption, bone growth, and which may be important in prostate cancer prevention). Our circadian rhythms are primarily regulated by the cyclic activity of sunlight exposure and are vital for healthy sleep-wake cycles, hormonal release, eating habits, and many other important physiological systems. During the winter months, many people suffer from “Seasonal Affective Disorder (SAD), a form of depression caused by reduced sunlight exposure. In fact, sunlight exposure on the skin alone has been shown to improve our mood.

Now “the bad”: How the sun’s ultraviolet radiation harms us

Beyond the visible light spectrum that we perceive with our eyes, there are invisible, higher-frequency electromagnetic energy waves produced by the sun called ultraviolet radiation (UVR). The sun’s UVR has energy strong enough to damage the cellular DNA of our skin and mucous membranes, which causes sunburns, photoaging (ie. wrinkles, sun spots), skin cancer, and damage to our eyes.


The 3 types of UVR (-A, -B, and –C) are distinguished based on their energy frequencies (the higher the frequency, the more damaging the energy). Thankfully most of the sun’s UV-C is blocked by the ozone layer.


UV-A (lower frequency): This makes up about 95% of the total UVR we are exposed to and it penetrates more deeply into the skin (ie. dermis) causing oxidative damage, DNA damage, and premature skin aging (ie. photoaging). UV-A also damages the basal cells of the epidermis, which predisposes to skin cancer. UV-A penetrates clouds, glass, and has relatively equal intensity during all daylight hours throughout the year. We are much more exposed to UV-A throughout our lifetime.


UV-B (higher frequency): This causes more damage to the surface of the skin (ie. epidermis) which results in sunburns and skin cancer. This is because UV-B damages cellular DNA and reduces the skin’s immune function.

Unprotected and excessive sun exposure increases the risk of skin cancer

Skin cancer is the most common form of cancer in Canada and is also one of the most preventable. The three most common types of skin cancer are basal cell carcinoma, squamous cell carcinoma, and melanoma. Basal cell is the most common, but overall the least aggressive of the three cancers. Melanoma is the most dangerous and can be fatal if it spreads to other parts of the body. Public health research demonstrates that Canadians are spending more time in the sun without protection and this is estimated to increase the number of melanoma cases by 72% over a 25-year period based on current trends.


Exposure to UVR when you’re young (particularly before age 20) is most harmful. There are studies that show a higher risk of melanoma in those who suffered sunburns during adolescence. The cumulative and more recent sun exposure predisposes to actinic keratoses (precancerous lesions that can turn into squamous cell carcinoma).

How would I know if I have skin cancer?

If you have any lumps or bumps on your body that are elevated, bleed, increase in size, or darken in color, then you must have them evaluated by your physician because these signs may suggest that the skin lesion is cancerous or precancerous. Unfortunately, the incidence of skin cancer in North America is on the rise as the effects of sun exposure continues to be detrimental and we expect these trends to continue so it’s always better to be safe and have a suspicious lesion examined by a professional.

How does sun exposure affect our eyes?

The eyes must also be protected from excessive sun exposure because UVR causes premature clouding of the lens (cataracts), eye surface degenerative changes that can decrease vision (ie. pterygium), increases the risk of vision loss from macular degeneration, and increases the risk for eye surface and eyelid cancer.

Who needs to protect themselves from UVR damage?

The simple answer is everyone, including those with darker skin types. However, certain populations such as children and the immunosuppressed are most at risk.

Take extra precaution if you have:

  • very fair skin
  • blond, red, or light brown hair
  • multiple moles (especially greater than 20), moles larger than 5mm, or moles present since birth
  • suffered from severe sunburns early in life
  • a hereditary condition such as xeroderma pigmentosum, Gorlin syndrome, or lupus
  • a prior history or family history of skin cancer
  • history of radiation treatment for psoriasis or other conditions
  • recently taken medications which make you more sun-sensitive (eg. antibiotics in the tetracycline family, oral contraceptives, anti-inflammatory drugs, etc).

What is the UV Index? Are certain times of the day safer to be outside?

The UV Index ranges from 0 to 11+ and is an international standard measurement of the strength of sunburn-producing UVR (the higher the number, the more UVR). This index is updated with your daily weather report and a value greater than or equal to 3 indicates “moderate risk”. In Canada, the UV Index is typically greater than 3 between April to September from 11am to 3pm. These are times when you need to avoid being outdoors or take extra precautions for sun safety (more below). Note that UVR is harmful to the skin even on cloudy days and is harmful to the eyes throughout the day and all year round.

Are tanning beds safer than direct sunlight?

Tanning beds are known to be UVR-emitting devices and UVR is classified as a carcinogen. Therefore, tanning beds are not at all safe and will increase your risk of developing skin cancer. The tan occurs once UVR has damaged the upper layer of the skin (epidermis). With prolonged exposure, the skin eventually burns (ie. turns red and may become painful or blister). Although the sun is the only natural source of UVR, devices such as tanning beds can generate even more UVR than sunlight, making them even more dangerous.


So how can I be safe and still enjoy the sun?

Sun Safety Recommendations

Although it’s impractical to prevent all exposure to UVR from sunlight, it is important to do your best to minimize the effects of sun exposure. This is because any amount of UVR is unsafe, irrespective of your skin type. Consider using as many of the suggestions below as you can to protect yourself, especially if you plan to be outdoors for longer periods of time. Protection is even more important for children and those with a suppressed immune system.

  • Shade. Seek shade or bring your own (eg. umbrella). Good quality options include dense vegetation or canopies with tightly-woven fabric. Ideally, you want protection overhead and from the sides.
  • Clothing. Wear clothing that covers as much skin as possible. Look for clothing labeled “UV protective” or which is tightly woven because this is more protective than sunscreen. A wide-brimmed hat is very effective and should cover the scalp, neck, ears, and face.
  • Eyewear. Wear sunglasses or prescription glasses labeled “UV400” or “100% UV protection” so that all UV-A and UV-B light is filtered. Close-fitting, wrap-around sunglasses will provide the best protection. A wide-brimmed hat is also protective for the eyes. Note that eye protection is required all-year-round and throughout the day, especially when exposed to highly reflective surfaces (eg. snow, sand, or water). UV-protective contact lenses do not provide sufficient protection.
  • Sunscreen. This should be labeled “broad-spectrum” and “water-resistant” with a sun protective factor (SPF) of 30 or greater. SPF 30 blocks 96.67% of UVR. In Canada, “water-resistant” labeling indicates you have about 40 mins of protection before you need to reapply. Generously apply sunscreen to all areas not protected with clothing and remember to reapply consistently depending upon duration of sun exposure. The average adult requires 2-3 tablespoons of lotion-formulated sunscreen to cover the entire body and 1 teaspoon to cover the face and neck. You must definitely reapply after being in water, toweling off, or sweating excessively. Also consider using lip balm with SPF in it. Remember to toss out any expired sunscreen products from last year because they do lose efficacy over time and it’s not worth taking the risk.

Don’t try to tan. Avoid deliberately trying to tan from sun exposure or tanning beds and definitely avoid getting a sunburn.

Sources of vitamin D. Rely on sources of vitamin D that are safer than sun exposure (eg. vitamin D fortified foods or supplements).


Plan your outdoor activities. Check the daily UV Index to prevent being outdoors when the UV index is 3 or greater (especially important for children). In Canada, this usually occurs between 11am and 3pm between April and September so it’s best to plan activities outside of these times.


Reducing your exposure to UVR from the sun and other sources is the best way to prevent premature “skin aging, eye damage, and skin cancer. Remember that you need to protect yourself all year round, even on cloudy days using the tips outlined above. Don’t rely on sun exposure as your primary source for vitamin D  because the risks far outweigh the benefits. Rather, eat foods fortified with vitamin D or take supplements. By adopting good sun-protection practices, you will be able to enjoy being outdoors this summer without putting your skin or eye health at risk.


Note: Dr. “H. Gill MD is an Assistant Professor of Ophthalmology at the University of Toronto and represented the Canadian Ophthalmological Society (COS) as part of a scientific panel along with researchers and physicians to help develop the Sun Safety National Consensus Report published in the Canadian Journal of Public Health in 2016.


Reference: Can J Public Health 2016;107(4-5):e473–e479 doi:10.17269/CJPH.107.5556

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