Ultraviolet (UV) index and sun safety

The ultraviolet (UV) index scale

The UV index scale tells you how strong the sun’s UV rays are. The amount of UV you get depends on the sun's strength and how long you spend in the sun. The higher the UV index, the more the sun’s rays can harm your skin and eyes.

Levels of the UV index

We group the UV index values into five risk levels:

• Low (0-2)
• Moderate (3-5)
• High (6-7)
• Very High (8-10)
• Extreme (11+)

Low: UV index levels 0 - 2

• low UV poses minimal risk, except when it’s bright and there is snow on the ground
• even with a low UV level, when it's bright and there is snow on the ground, you can get almost twice as much UV
• fresh white snow can reflect over 80% of the sun's UV rays
• wear UV protection sunglasses to help protect your eyes
• cover up your skin and use sunscreen if you are outside for more than one hour during bright, snowy days

Moderate to high: UV index levels 3 - 7

• wear a hat that covers your face and ears and tight woven clothes (like linen) to cover your skin
• put sunscreen on skin that you cannot cover
• in cool or slightly cloudy weather, you still need to protect yourself- the UV still get through
• look for shade when the sun is the strongest near midday

Very high to extreme: UV index levels of 8 or more

• do not stay too long in the sun, especially between 11 a.m. and 3 p.m.
• wear UV protection sunglasses and stay in the shade
• reapply sunscreen every 2 hours or after you swim or sweat a lot
• unprotected skin can burn quickly on clear, sunny days

Find your ultraviolet (UV) forecast

The UV forecast shows the highest amount of UV you can expect for the day. Find your forecast:

• first, choose your city or area on the weather forecast page
• next, look for the text description of the seven-day forecast in the “Forecast” box
• note: you can also find the UV forecast in the WeatherCAN app in the “7 Day” tab

The most dangerous times for ultraviolet (UV) rays

When the sun’s rays are strongest, you get more UV and you can get sunburned faster. UV rays from the sun are linked to sunburns, eye problems, skin aging, and skin cancer. 

In Canada, UV exposure risk is highest:

• from 11 a.m. to 3 p.m.
• from April to September
• when the UV is at level 3 or higher
• during sun or cloud (even when it's cloudy, UV can cause burns)

Additional risk factors for UV exposure:

• snow, dry sand, and concrete: light-coloured surfaces reflect the sun’s rays like a mirror, and increase the amount of UV you get
• mountains: more UV reaches higher places because the air is thinner and clearer
• time in the sun: the longer you are outside in the sun, the more UV you get

How to stay safe from ultraviolet (UV) rays

Take steps to protect your skin and your eyes. Keep children and toddlers safe, and remember to protect yourself when you travel on holiday

Protect your skin

• look for shade or bring your own (like an umbrella or UV beach shelter tent)
  • you can reduce the UV you get by 50% or more in the shade
• wear clothes that cover most of your skin
  • wear a wide-brimmed hat, if it fits your activity and the weather or a cap for sports
  • consider wearing UV protective clothing or a rash guard with long sleeves if you are doing water activities
• use sunscreen that says "broad spectrum" and "water resistant"
  • you need an SPF of at least 30 on uncovered skin
  • put on plenty of sunscreen, reapply every 2 hours
• do not get a sunburn
  • do not try to get a tan on purpose
  • if you have a sunburn, apply aloe or flax seed gel to sooth and cool skin
• Health Canada does not recommend using tanning beds (especially for people under 18 years old)

Protect your eyes

• wear sunglasses or eyeglasses with UV protective lenses
• wear a wide-brimmed hat to protect your eyes even more

Sun safety for children and travellers

• babies and small children burn easily because they have sensitive skin—make sure you protect them from the sun
• be careful on winter trips in the sun

Seasonal UV exposure

The sun’s rays become stronger as you go south. Canada’s highest numbers on the UV Index Scale are found in southern Ontario.  

Winter

• the UV index in Canada is generally low in winter (except when snow reflects UV to almost double the index value)
• skiing and other outdoor winter activities can increase the UV you get
• if you are skiing in the mountains, you will get more UV because of the higher elevation

Spring

• in Canada, the UV Index is highest in the spring and summer
• April is a good time to start taking more steps to stay safe
• fresh white snow in the spring can reflect over 80% of the sun’s UV rays (you get almost twice as much UV)
• wear ski goggles to protect your eyes
• put sunscreen on any skin that shows

Summer

• the sun is strongest in the summertime
• think about doing outdoor activities, like biking, before 11 a.m. or after 3 p.m.
• be extra careful at the beach—you can sunburn quickly because the sun can reflect off the water and light-coloured sand
• cover up and try to spend less time in the sun
• bring a beach umbrella or find some shade
• make sure to reapply sunscreen every two hours or after you swim or exercise

Fall

• the UV Index can be high in early September, but it quickly goes down by October
• UV exposure is generally not a concern until the snow falls

Sun safety at school and in your community

Young people are especially sensitive to sun. They spend time outside when the sun is strong, especially during lunches, recess, and sports.

Sunburn damage will stay with you for life and can lead to even more dangerous problems later in life. Public health and safety includes helping young people protect themselves from the sun. This will help prevent serious health problems.

At school or in your community, you can:

• organize outdoor activities outside the strongest sun hours of 11 a.m. to 3 p.m.
• try to keep children completely out of the sun from noon to 2 p.m. (if possible)
• get free UV posters and wallet cards  

How we calculate the ultraviolet (UV) index and create forecasts

The UV index is based on:

• the thickness of the ozone layer high in the atmosphere
  • a thick ozone layer absorbs more UV
  • natural changes can alter its thickness each day
• the sun's angle above the horizon
  • when the sun is high overhead, its rays travel straight down towards the ground, the shortest path through the atmosphere—this is when UV is strongest
  • when the sun is closer to the horizon, its rays travel further through the atmosphere—less UV reaches the ground when the sun is lower in the sky
• the amount of cloud cover
  • thick clouds can reduce the amount of UV

To create the UV forecast:

• first, ozone monitoring stations measure the current thickness of the ozone layer and a computer model predicts ozone levels for the next day
• next, we combine the ozone level forecast with the sun's height and angle to estimate UV levels under clear skies
• finally, we factor in the expected cloud cover to determine the UV levels people will experience

The UV index: a Canadian success story

Scientists at Environment and Climate Change Canada created the UV index in 1992. They wanted a tool to help protect Canadians from too much sun. The scientists set the first UV index scale from zero to 10. They based this on the UV values usually found in Canada.

In 1994, the World Health Organization (WHO) and the United Nations Environment Program saw the value of Canada’s UV index and made it an international program. In 2002, they created a global standard, using the Canadian model. People now use it around the world. UV values in more southerly countries can be much higher than those in Canada, so the WHO and its partners decided to make the scale open-ended. This way, it can go over 10. You can find UV index values up to 14 in tropical countries.

Related resources

• Health effects of UV radiation
• Types of skin cancer and preventing skin cancer
• UV poster and wallet cards
• Canadian Cancer Society
• Ozone data (World Ozone and Ultraviolet Radiation Data Centre)