Cancer de la peau et le soleil

Health Canada states that one of the main causes of skin cancer is ultraviolet (UV) light, which is produced by the sun and tanning equipment.

Skin cancer is an occupational concern for people who work under the sun. The risk however, may be reduced through awareness of the problem, and by taking measures to prevent exposure to sunlight.

Yes. The types of radiation include:

• visible light, which gives us the colours we see
• infrared radiation which gives us the warmth we feel
• ultraviolet (UV) radiation

Except in extreme situations, neither visible light nor infrared radiation from sunlight causes health problems. However, ultraviolet (UV) radiation can cause harmful effects to the skin.

There are three basic types of ultraviolet radiation:

• UVA (long-wave UV)
• UVB (sunburn UV)
• UVC (short-wave UV)

When ultraviolet radiation reaches the skin, some radiation is reflected away from the surface. The remaining radiation is scattered into the tissues just beneath the skin's surface. A fraction of this radiation is absorbed by the skin's living cells.

Ultraviolet radiation absorbed by living cells damages sensitive substances that influence the skin's normal growth and appearance. Damage can result in:

• sunburn
• increased rate of aging of the skin
• skin cancer

Sunburn

Sunburn is the most familiar and immediate effect of ultraviolet radiation on the skin. It is an inflammation caused by an increase in blood-flow beneath the skin. The reaction is not normally instantaneous, but reaches a bright red colour within 15 to 20 hours. The condition can be very painful and sometimes causes peeling of the skin.

Brief intense exposure can cause severe sunburn in people who are not accustomed to strong sunlight. There is evidence that this type of exposure, as well as long-term exposures, might be linked to serious forms of skin cancer later in life.

Increased Rate of Aging of the Skin

Repeated exposure to the sun's ultraviolet radiation eventually causes skin damage similar to the aging process. Patches of skin become thin and less elastic, and develop blemishes, sun freckles, and wrinkles. These changes may take many years of exposure but when they occur, the damage is irreversible.

Skin Cancer

If exposure to sunlight continues for several years, the damaged skin has an increased chance of developing one of the forms of skin cancer. Exposure to ultraviolet radiation increases the risk of developing these cancers (although it may not be the only cause of the disease). Health Canada states that many studies have shown that people who have had many severe sunburns in childhood are at greater risk of developing skin cancer.  Family history, some chemical exposures, and immune dysfunction conditions can also create a greater risk of developing skin cancer.

Three different types of skin cancer are linked to sunlight exposure:

• basal cell cancer
• squamous cell cancer
• malignant melanoma

Basal Cell Cancer

Basal cell cancer is the most common of all cancers in North America and Europe. It is usually found in areas of the skin exposed to sunlight, but sometimes occurs in other areas as well. This type of skin cancer appears as a raised, hard, red or red-grey, pearly wound often found on the forehead, eyelids, cheeks, nose, and lips. Although there is always a chance it could become serious, basal cell cancer usually does not spread. Most cases are easily treated.

Squamous Cell Cancer

Squamous cell cancer occurs most frequently on the skin exposed to sunlight over long periods of time. As such, this type of skin cancer tends to develop where maximum exposure to radiation occurs - forehead, cheeks, nose, lower lip, and tops of the ears. It also usually develops in areas where the skin has been damaged by the sun - areas with blemishes or sun freckles. The blemishes develop into rough, scaly patches with small areas of open wounds that do not heal. They eventually grow into larger wounds with crusts. Similar to basal cell carcinoma, most cases are easily treated.

Malignant Melanoma

Malignant melanoma, although rarer, is the most serious of the skin cancers. It often shows itself as a mole or pigment spot that begins to bleed, grow, or change its colour, shape or texture. It usually spreads if not treated in the early stage. If caught early, malignant melanoma can be treated. If treatment is delayed,  melanoma can be hard to stop once it has spread to other parts of the body. Melanoma is the type most likely to be fatal.

Everyone is at risk of skin cancer. Risk factors include:

• exposure to ultraviolet radiation (UV)
• heredity and medical factors, such as:
  • having many moles, or certain types of moles on your skin
  • having fair or light-coloured skin (these individuals have less melanin which may help protect the skin)
  • history of skin cancer in self or family
  • specific medical conditions, such as CDKN2A gene mutation
  • weakened immune system

Another factor may include exposure to chemicals. Exposure to certain chemicals can increase the skin's sensitivity to ultraviolet light through a process called photosensitization. Examples of such chemicals include:

• coal tar, coal tar pitches, and petroleum products containing polycyclic aromatic hydrocarbons (PAHs)
• certain printing chemicals used in photosensitive printing processes
• certain drugs including antibiotics, oral contraceptives, anti-inflammatories, tranquilizers, and anti-nausea drugs
• chemicals called psoralens found naturally in certain plants, fruits and vegetables

Check with your physician or pharmacist if you suspect abnormal or severe reaction to sun exposure after taking new medication. However, simple skin contact with psoralens, which are found in figs, parsnips, citrus plants, or mouldy celery, can make the skin more susceptible to sunburns in some individuals.

Experimental studies show that chemicals called "promoters" can increase the cancer-causing ability of ultraviolet radiation. On the other hand, ultraviolet radiation itself can act as a promoter. In particular, ultraviolet radiation (UVR) can increase the cancer-causing ability of chemicals from coal tar and coal tar pitches.

Does the amount of exposure to sunlight matter?

Yes. The damaging effects of ultraviolet radiation accumulate over the years. In general, the risk of developing skin cancer increases with the amount of time spent under the sun and the intensity of radiation. The intensity of radiation varies according to the season of the year, time of day, geographic location (latitude), elevation above sea level, reflection from surfaces (e.g., white sand or concrete, water, snow), stratospheric ozone, clouds, and air pollution.

Studies have focused on the effects of intermittent (short-term, occasional) sun exposure in comparison to chronic (long-term) exposure. It appears that the type of exposure may influence the type of cancer that develops. For example, intermittent solar exposure may be an important factor leading to the onset of basal cell carcinoma of the skin. Childhood sun exposure may also play an important part in the development of these cancers later in adult life. The pattern for cutaneous melanoma is similar to that for basal cell carcinoma.

In contrast, the relationship between squamous cell carcinoma and solar UVR appears to be quite different. For squamous cell tumours, high levels of chronic occupational sunlight exposure, especially in the 10 years before diagnosis, results in an elevated risk for this cancer in the highest exposure group.

In order to address the growing concern by Canadians regarding changes in UVR resulting from ozone depletion, Environment and Climate Change Canada rates the UV intensity as UV Index on a scale of 0 (when there is no sunlight) to 11+ (extreme). It can go to the mid-teens at midday in the tropics. In Canada the UV Index is categorized into low (2 or less), moderate (between 3 and 5), high (between 6 and 7), very high (between 8 and 10) and extreme (greater than 11).

The human health effects and precautions relating to the UV Index are summarized in the following table.

Source:

The UV Index Poster: Environment and Climate Change Canada

All outdoor workers potentially exposed to the sun's ultraviolet radiation are at risk, including:

• agricultural workers
• farmers
• horticultural workers
• maintenance workers
• pipeline workers
• ranchers
• athletes
• fishermen
• landscapers
• military personnel
• police
• ski instructors
• brick masons
• gardeners
• lifeguards
• oilfield workers
• postal carriers
• sailors
• construction workers
• greenskeepers
• loggers
• open-pit miners
• railroad track workers
• surveyors

Indoor workers exposed to UV would include those in tanning salons or where UV-producing devices are used (e.g., medicine, cosmetics, etc.).

It is important to be aware of the risks and take precautions while under the sun from as early in life as possible. Approaches to prevent skin cancer include:

• reducing exposure to sunlight
• wearing protective clothing
• using sunscreens on exposed skin
• examining the skin regularly for suspicious spots

In the winter time, it may be advisable to the above precautions when exposed to sun for prolonged periods, especially in the presence of snow or at high altitudes.

Reducing Exposure

Workers should avoid unnecessary exposure to the sun, especially to the intense midday rays between 11:00 a.m. and 3:00 p.m. during the summer. If possible, people should plan outdoor work for early morning or late afternoon, and work in the shade as much as possible. Umbrellas, buildings, shade structures, trees, canopies, etc., can protect against the direct rays from the sun. Work, and take breaks in the shade when ever possible. Set up shade structures when shade is not available. In addition, water, white sand or concrete, snow, and ice can reflect from around 10 percent to 85 percent of the sun's ultraviolet radiation. Skin may require extra protection against these indirect, reflected rays.

Workplaces can also rotate workers between site locations to help reduce UV exposure.

Wearing Protective Clothing and Sunglasses

The use of wide brim hats and clothes made from close-knit fabric can protect the skin and scalp from ultraviolet radiation. Although long-sleeved shirts and long-legged pants may not be comfortable in extremely hot weather, they do help protect the skin. Clothing specifically designed to be sun protective or sun blocking will indicate the protection rating (a UV protection factor, or UPF).  Be aware that not all clothing offers the same protection.  Factors include the colour of the clothing, construction, materials the item is made from, fit, and coverage over the body.  Some fabrics lose their SPF rating when they get wet. Workers should be informed about different fabric characteristics that effect the transmission of sunlight.

Wear wrap-around sunglasses that absorb UVA and UVB radiation.

Using Protective Sunscreens

Workers should liberally apply protective sunscreen on exposed skin 20 minutes before working in the sun, then reapply it during the periods they spend under the sun, as directed by the manufacturer's instructions (usually every two hours). Most sunscreens are colourless, invisible, and cosmetically acceptable.

Sunscreens should be used in addition to, not instead of, working in shade and wearing suitable clothing, hats, and sunglasses. Sunscreens are not intended to extend the exposure time to sunlight, but rather to reduce the effects of sunlight when people have to be in the sun. The level of protection depends greatly on how the sunscreen is applied.

A wide variety of sunscreens are available. They all contain chemical ingredients that weaken (but do not eliminate) the effects of ultraviolet radiation. The most widely used protective chemicals are PABA (para-aminobenzoic acid) and closely related chemicals such as cinnamates, salicylates, benzophenones, or anthranilates. Some sunscreens contain only one of these protective chemicals while others may have two or more for greater reliability.

Manufacturers label sunscreens with a sun protection factor (SPF). The higher the factor, the greater the protection from the sun.

• SPF 15 sunscreen may absorb 93 percent of UVB radiation.
• SPF 30 sunscreen may absorb 97 percent of UVB radiation.

The Canadian Cancer Society recommends a broad spectrum sunscreen (protects against UVA and UVB rays) with an SPF of 30 or higher. Follow the manufacturer’s directions. A sunscreen's effectiveness also depends upon its ability to withstand heat, humidity and sweat. For example, sunscreens should be applied 20 minutes before going outdoors, and reapplied every two hours, or more often if perspiring (sweating), swimming, or working in water. Use a broad spectrum lip balm with an SPF of 30 or higher as well.

People with skin sensitive to sunlight should use a sunscreen with a high SPF.

Examining Skin Regularly

People who work under the sun should examine their skin regularly for any unusual changes. The danger signs include any wound, sore, or patch of skin that won't heal or constantly scales. Also examine for any growing lump, particularly if brown or bluish in colour. It is important to get medical care for anything that looks suspicious rather than wait until the problem becomes untreatable.