As I was sitting on a patio this past Sunday, enjoying what felt like one of the first nice days of the summer Toronto's had this year, the table next to me started a conversation about how they had recently heard about record ozone loss above the Arctic this past winter and how it will effect ultraviolet rays here in Toronto. I was advised to wear a lot of sunscreen this summer.
This inspired me to write an article about how these climate changes affect our health.
ULTRAVIOLET RADIATION

Ultraviolet (UV) radiation is a type of electromagnetic radiation that is not visible to the human eye. It is named “ultraviolet” because the electromagnetic rays are of higher frequencies than what humans identify as the colour violet.
It is subdivided into different ranges according to wavelength, including ultraviolet A (UVA) or long wave, ultraviolet B (UVB) or medium wave, and ultraviolet C (UVC) or short wave.
Sunlight is the greatest source of UV radiation. Other sources, which are man-made, include UV lamps, arc welding, and mercury vapour lamps.
The sun's emission of UV rays is relevant because the sun emits ultraviolet radiation in the UVA, UVB, and UVC bands, and each band type has different effects on our health.
Positive effects of skin exposure to the sun are attributed to UVB rays. UVB induces the production of vitamin D, which is responsible for maintenance of bone density, bone growth, and normal functioning of the nervous system.
Vitamin D also regulates immunity, cell proliferation, insulin secretion, and blood pressure. UV exposure has also been suggested to positively benefit cases of rickets, psoriasis, eczema, vitiligo, and lupus.
Negative effects of sun exposure are associated with UVB and UVA rays. UVB rays reach the outer layer of the skin (epidermis) and too much UVB radiation exposure can cause direct DNA damage, sunburn, premature aging of the skin, and skin cancer.
UVA reaches the middle layer of the skin (dermis) but is considered to be less harmful than UVB as it does not cause sunburns but can contribute to skin cancer through indirect DNA damage. Both UVA and UVB also destroy vitamin A in skin, which may cause further damage.
Of the UV rays, UVC is the most dangerous type and is capable of causing mutagenic or carcinogenic effects but is not of concern in the context of sun exposure because it is filtered out by the atmosphere and does not reach the surface of the Earth.
CLIMATE CHANGE AND OZONE DESTRUCTION
In recent years, climate change has been in the forefront of media (e.g. the movie An Inconvenient Truth). A result of climate change is the formation of ozone-destroying chemical reactions. As our emissions increase (from products such as refrigerators, aerosol spray cans, and fire extinguishers), green house gases trap heat close to the surface of the earth, preventing heat to reach the above stratosphere. This causes the temperature in the stratosphere to be cooler which encourages depletion of the ozone.
This year, ozone loss in the arctic has reached a record high.
OZONE DESTRUCTION AND ULTRAVIOLET RADIATION
Naturally, the Earth's ozone layer blocks the majority of UV radiation emitted by the sun by preventing it from penetrating through the atmosphere. Due to the destruction of the ozone layer, more UV radiation is reaching the surface of the earth, thus, increasing our exposure to UV rays.
PREVENTION
With the destruction of the ozone, it is important to have appropriate protection from sun exposure to prevent the damaging effects of UV radiation exposure.
Environmental Canada and World Health Organization developed the UV index: a measurement of the intensity of UV radiation from the sun that reaches the surface of different locations on the Earth. Note that intensity is variable, depending on how high the angle of the sun is in the sky.
It is important to note the UV Index daily before going outdoors, and implement protection as discussed.
UV INDEX
- 0-2: UV radiation levels pose no danger to the average person, but it is recommended to wear sunglasses, sunscreen/sunblock if there is snow on the ground as it reflects UV radiation, or if you are particularly fair.
- 3-5: There is some risk of harm from unprotected sun exposure. Recommendations include sunglasses and use of SPF 30+ sunscreen/sunblock.
- 6-7: There is a high risk of harm from unprotected sun exposure. Recommendations include sunglasses, use of SPF 30+ sunscreen/sunblock, covering the body with protective clothing, and avoiding sun exposure between 11:00AM to 4PM during the summer.
- 8-10: There is a very high risk of harm from unprotected sun exposure. Wear SPF 30+ sunscreen/sunblock, a shirt, sunglasses, and hat. Avoid sun exposure between 11:00AM and 4PM during the summer, and do not stay out in the sun for long periods of time.
- 11+: There is an extreme risk of harm from unprotected sun exposure. Take all precautions including sunglasses, SPF 30+ sunscreen/sunblock, cover the body with long-sleeve shirt, trousers, and a broad rimmed hat. Do not stay out in the sun for long periods of times, and avoid the sun during peak times.
Toronto has already reached days with a UV Index of 9 and is expected to have 11+ days this summer!
As summer approaches, it is important to determine what type (sunscreen or sunblock) and strength (SPF) of protection to use. There are many misconceptions of both.
SUNSCREEN/SUNBLOCK
Contrary to popular belief, sunscreen and sunblock are not the same thing. There is a very important difference: sunscreen is a product that acts as a filter, allowing a certain range of UV light to be absorbed in the skin, and contains chemicals that absorb and reflect particular UV rays so that they do not reach the skin. Sunblock contains materials such as titanium dioxide or zinc oxide that physically block and reflect UV rays, therefore acting as a wall between the skin and the sun.
Sunscreen can protect against UVA and UVB rays, using chemicals such as avenobenzone, oxybenzone, and octocrylene. However, the cocktail of chemicals that are used, contain ingredients that are known or suspected carcinogens and/or hormone disrupters.
The preferred form of protection is sunblock, because it can provide “broad spectrum UV protection” or in other words, blocks both UVA and UVB rays, without the use of carinogenic and hormone disrupting ingredients depending on the mineral used.
Titanium dioxide is one of the two main ingredients in sunblock, but sunblocks containing this mineral should not be applied to children's bodies on a regular basis, as it can cause DNA damage and can be carcinogenic. Zinc oxide is the only FDA approved sunblock for use on children under 6 months of age, as it is considered to be safe and furthermore, has anti-inflammatory properties.
The only con of using zinc oxide is that the regular form of zinc oxide leaves a strong white residue on the skin which consumers may find unappealing. In order to compensate, zinc oxide sunblock now uses nano-sized particles, which raises the concern of skin absorption and phototoxicity in pregnant women. Recent research shows that nanoparticles can cross the human placenta, possibly exposing the developing fetus to zinc oxide, but the effects of this have not been studied.
SUN PROTECTION FACTOR (SPF)
SPF is a measure of the effectiveness of sunscreen and sunblock. It represents the amount of UVB exposure required to cause a sunburn when applied to the skin, so the higher the SPF, the more protection it provides against ultraviolet radiation.
Consumers typically misunderstand SPF, believing that for example, a SPF 15 means that they are able to stay in the sun for 15 hours without getting a sunburn (15 times longer), but this is not true. Although UV radiation exposure is related to time, there are other influential factors, including:
- time of day (in Canada, UV intensity is at its maximum between 12 and 1PM)
- season (spring and summer are most intense),
- weather conditions (heavy cloud coverage absorb some UV radiation)
- skin type (melanin is the pigment that makes skin darker and absorbs UV radiation, so fairer skin has less melanin and thus less protection)
- amount applied and frequency of re-application of sunblock/sunscreen
- the activities in which one engages (such as swimming)
- the amount of skin absorption.
It is also important to note that SPF is imperfect as it only considers UVB exposure, but UVA also causes invisible damage which can lead to cancer.
SO WHAT MEANS OF PROTECTION SHOULD BE IMPLMENTED?
The WHO encourages 10-15 minutes of sun exposure per day to ensure Vitamin D production. If more time is spent in the sun, follow the recommendations according to the UV Index including minimizing exposure. If the UV Index is 3 or higher, sunblock of SPF 30+ which uses zinc oxide, that has not been modified to nanoparticles for use by pregnant women, apply according to skin type and intensity of UV Index, and reapply depending on activities and absorption.
Dr. Cristina